RDMA/mlx5: Initialize the ODP xarray when creating an ODP MR

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

RDMA/mlx5: Initialize the ODP xarray when creating an ODP MR

Normally the zero fill would hide the missing initialization, but an
errant set to desc_size in reg_create() causes a crash:

BUG: unable to handle page fault for address: 0000000800000000
PGD 0 P4D 0
Oops: 0000 [#1] SMP PTI
CPU: 5 PID: 890 Comm: ib_write_bw Not tainted 5.15.0-rc4+ #47
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
RIP: 0010:mlx5_ib_dereg_mr+0x14/0x3b0 [mlx5_ib]
Code: 48 63 cd 4c 89 f7 48 89 0c 24 e8 37 30 03 e1 48 8b 0c 24 eb a0 90 0f 1f 44 00 00 41 56 41 55 41 54 55 53 48 89 fb 48 83 ec 30 <48> 8b 2f 65 48 8b 04 25 28 00 00 00 48 89 44 24 28 31 c0 8b 87 c8
RSP: 0018:ffff88811afa3a60 EFLAGS: 00010286
RAX: 000000000000001c RBX: 0000000800000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000800000000
RBP: 0000000800000000 R08: 0000000000000000 R09: c0000000fffff7ff
R10: ffff88811afa38f8 R11: ffff88811afa38f0 R12: ffffffffa02c7ac0
R13: 0000000000000000 R14: ffff88811afa3cd8 R15: ffff88810772fa00
FS: 00007f47b9080740(0000) GS:ffff88852cd40000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000800000000 CR3: 000000010761e003 CR4: 0000000000370ea0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
mlx5_ib_free_odp_mr+0x95/0xc0 [mlx5_ib]
mlx5_ib_dereg_mr+0x128/0x3b0 [mlx5_ib]
ib_dereg_mr_user+0x45/0xb0 [ib_core]
? xas_load+0x8/0x80
destroy_hw_idr_uobject+0x1a/0x50 [ib_uverbs]
uverbs_destroy_uobject+0x2f/0x150 [ib_uverbs]
uobj_destroy+0x3c/0x70 [ib_uverbs]
ib_uverbs_cmd_verbs+0x467/0xb00 [ib_uverbs]
? uverbs_finalize_object+0x60/0x60 [ib_uverbs]
? ttwu_queue_wakelist+0xa9/0xe0
? pty_write+0x85/0x90
? file_tty_write.isra.33+0x214/0x330
? process_echoes+0x60/0x60
ib_uverbs_ioctl+0xa7/0x110 [ib_uverbs]
__x64_sys_ioctl+0x10d/0x8e0
? vfs_write+0x17f/0x260
do_syscall_64+0x3c/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae

Add the missing xarray initialization and remove the desc_size set.