RDMA/hns: Fix NULL pointer problem in free_mr_init()

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

RDMA/hns: Fix NULL pointer problem in free_mr_init()

Lock grab occurs in a concurrent scenario, resulting in stepping on a NULL

pointer. It should be init mutex_init() first before use the lock.

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000

Call trace:

__mutex_lock.constprop.0+0xd0/0x5c0

__mutex_lock_slowpath+0x1c/0x2c

mutex_lock+0x44/0x50

free_mr_send_cmd_to_hw+0x7c/0x1c0 [hns_roce_hw_v2]

hns_roce_v2_dereg_mr+0x30/0x40 [hns_roce_hw_v2]

hns_roce_dereg_mr+0x4c/0x130 [hns_roce_hw_v2]

ib_dereg_mr_user+0x54/0x124

uverbs_free_mr+0x24/0x30

destroy_hw_idr_uobject+0x38/0x74

uverbs_destroy_uobject+0x48/0x1c4

uobj_destroy+0x74/0xcc

ib_uverbs_cmd_verbs+0x368/0xbb0

ib_uverbs_ioctl+0xec/0x1a4

__arm64_sys_ioctl+0xb4/0x100

invoke_syscall+0x50/0x120

el0_svc_common.constprop.0+0x58/0x190

do_el0_svc+0x30/0x90

el0_svc+0x2c/0xb4

el0t_64_sync_handler+0x1a4/0x1b0

el0t_64_sync+0x19c/0x1a0