mlxsw: spectrum_acl_tcam: Fix NULL pointer dereference in error path

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

mlxsw: spectrum_acl_tcam: Fix NULL pointer dereference in error path

When calling mlxsw_sp_acl_tcam_region_destroy() from an error path after

failing to attach the region to an ACL group, we hit a NULL pointer

dereference upon 'region->group->tcam' [1].

Fix by retrieving the 'tcam' pointer using mlxsw_sp_acl_to_tcam().

[1]

BUG: kernel NULL pointer dereference, address: 0000000000000000

[...]

RIP: 0010:mlxsw_sp_acl_tcam_region_destroy+0xa0/0xd0

[...]

Call Trace:

mlxsw_sp_acl_tcam_vchunk_get+0x88b/0xa20

mlxsw_sp_acl_tcam_ventry_add+0x25/0xe0

mlxsw_sp_acl_rule_add+0x47/0x240

mlxsw_sp_flower_replace+0x1a9/0x1d0

tc_setup_cb_add+0xdc/0x1c0

fl_hw_replace_filter+0x146/0x1f0

fl_change+0xc17/0x1360

tc_new_tfilter+0x472/0xb90

rtnetlink_rcv_msg+0x313/0x3b0

netlink_rcv_skb+0x58/0x100

netlink_unicast+0x244/0x390

netlink_sendmsg+0x1e4/0x440

____sys_sendmsg+0x164/0x260

___sys_sendmsg+0x9a/0xe0

__sys_sendmsg+0x7a/0xc0

do_syscall_64+0x40/0xe0

entry_SYSCALL_64_after_hwframe+0x63/0x6b