dpaa2-eth: retrieve the virtual address before dma_unmap

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

dpaa2-eth: retrieve the virtual address before dma_unmap

The TSO header was DMA unmapped before the virtual address was retrieved
and then used to free the buffer. This meant that we were actually
removing the DMA map and then trying to search for it to help in
retrieving the virtual address. This lead to a invalid virtual address
being used in the kfree call.

Fix this by calling dpaa2_iova_to_virt() prior to the dma_unmap call.

[ 487.231819] Unable to handle kernel paging request at virtual address fffffd9807000008

(...)

[ 487.354061] Hardware name: SolidRun LX2160A Honeycomb (DT)
[ 487.359535] pstate: a0400005 (NzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 487.366485] pc : kfree+0xac/0x304
[ 487.369799] lr : kfree+0x204/0x304
[ 487.373191] sp : ffff80000c4eb120
[ 487.376493] x29: ffff80000c4eb120 x28: ffff662240c46400 x27: 0000000000000001
[ 487.383621] x26: 0000000000000001 x25: ffff662246da0cc0 x24: ffff66224af78000
[ 487.390748] x23: ffffad184f4ce008 x22: ffffad1850185000 x21: ffffad1838d13cec
[ 487.397874] x20: ffff6601c0000000 x19: fffffd9807000000 x18: 0000000000000000
[ 487.405000] x17: ffffb910cdc49000 x16: ffffad184d7d9080 x15: 0000000000004000
[ 487.412126] x14: 0000000000000008 x13: 000000000000ffff x12: 0000000000000000
[ 487.419252] x11: 0000000000000004 x10: 0000000000000001 x9 : ffffad184d7d927c
[ 487.426379] x8 : 0000000000000000 x7 : 0000000ffffffd1d x6 : ffff662240a94900
[ 487.433505] x5 : 0000000000000003 x4 : 0000000000000009 x3 : ffffad184f4ce008
[ 487.440632] x2 : ffff662243eec000 x1 : 0000000100000100 x0 : fffffc0000000000
[ 487.447758] Call trace:
[ 487.450194] kfree+0xac/0x304
[ 487.453151] dpaa2_eth_free_tx_fd.isra.0+0x33c/0x3e0 [fsl_dpaa2_eth]
[ 487.459507] dpaa2_eth_tx_conf+0x100/0x2e0 [fsl_dpaa2_eth]
[ 487.464989] dpaa2_eth_poll+0xdc/0x380 [fsl_dpaa2_eth]