mtd: spi-nor: sst: Fix SST write failure

In the Linux kernel, the following vulnerability has been resolved:

mtd: spi-nor: sst: Fix SST write failure

'commit 18bcb4aa54ea ("mtd: spi-nor: sst: Factor out common write operation
to `sst_nor_write_data()`")' introduced a bug where only one byte of data
is written, regardless of the number of bytes passed to
sst_nor_write_data(), causing a kernel crash during the write operation.
Ensure the correct number of bytes are written as passed to
sst_nor_write_data().

Call trace:
[ 57.400180] ------------[ cut here ]------------
[ 57.404842] While writing 2 byte written 1 bytes
[ 57.409493] WARNING: CPU: 0 PID: 737 at drivers/mtd/spi-nor/sst.c:187 sst_nor_write_data+0x6c/0x74
[ 57.418464] Modules linked in:
[ 57.421517] CPU: 0 UID: 0 PID: 737 Comm: mtd_debug Not tainted 6.12.0-g5ad04afd91f9 #30
[ 57.429517] Hardware name: Xilinx Versal A2197 Processor board revA - x-prc-02 revA (DT)
[ 57.437600] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 57.444557] pc : sst_nor_write_data+0x6c/0x74
[ 57.448911] lr : sst_nor_write_data+0x6c/0x74
[ 57.453264] sp : ffff80008232bb40
[ 57.456570] x29: ffff80008232bb40 x28: 0000000000010000 x27: 0000000000000001
[ 57.463708] x26: 000000000000ffff x25: 0000000000000000 x24: 0000000000000000
[ 57.470843] x23: 0000000000010000 x22: ffff80008232bbf0 x21: ffff000816230000
[ 57.477978] x20: ffff0008056c0080 x19: 0000000000000002 x18: 0000000000000006
[ 57.485112] x17: 0000000000000000 x16: 0000000000000000 x15: ffff80008232b580
[ 57.492246] x14: 0000000000000000 x13: ffff8000816d1530 x12: 00000000000004a4
[ 57.499380] x11: 000000000000018c x10: ffff8000816fd530 x9 : ffff8000816d1530
[ 57.506515] x8 : 00000000fffff7ff x7 : ffff8000816fd530 x6 : 0000000000000001
[ 57.513649] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
[ 57.520782] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0008049b0000
[ 57.527916] Call trace:
[ 57.530354] sst_nor_write_data+0x6c/0x74
[ 57.534361] sst_nor_write+0xb4/0x18c
[ 57.538019] mtd_write_oob_std+0x7c/0x88
[ 57.541941] mtd_write_oob+0x70/0xbc
[ 57.545511] mtd_write+0x68/0xa8
[ 57.548733] mtdchar_write+0x10c/0x290
[ 57.552477] vfs_write+0xb4/0x3a8
[ 57.555791] ksys_write+0x74/0x10c
[ 57.559189] __arm64_sys_write+0x1c/0x28
[ 57.563109] invoke_syscall+0x54/0x11c
[ 57.566856] el0_svc_common.constprop.0+0xc0/0xe0
[ 57.571557] do_el0_svc+0x1c/0x28
[ 57.574868] el0_svc+0x30/0xcc
[ 57.577921] el0t_64_sync_handler+0x120/0x12c
[ 57.582276] el0t_64_sync+0x190/0x194
[ 57.585933] ---[ end trace 0000000000000000 ]---

[pratyush@kernel.org: add Cc stable tag]