xfs: fix memory leak in xfs_errortag_init

xfs: fix memory leak in xfs_errortag_init

When `xfs_sysfs_init` returns failed, `mp->m_errortag` needs to free.
Otherwise kmemleak would report memory leak after mounting xfs image:

unreferenced object 0xffff888101364900 (size 192):
  comm "mount", pid 13099, jiffies 4294915218 (age 335.207s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<00000000f08ad25c>] __kmalloc+0x41/0x1b0
    [<00000000dca9aeb6>] kmem_alloc+0xfd/0x430
    [<0000000040361882>] xfs_errortag_init+0x20/0x110
    [<00000000b384a0f6>] xfs_mountfs+0x6ea/0x1a30
    [<000000003774395d>] xfs_fs_fill_super+0xe10/0x1a80
    [<000000009cf07b6c>] get_tree_bdev+0x3e7/0x700
    [<00000000046b5426>] vfs_get_tree+0x8e/0x2e0
    [<00000000952ec082>] path_mount+0xf8c/0x1990
    [<00000000beb1f838>] do_mount+0xee/0x110
    [<000000000e9c41bb>] __x64_sys_mount+0x14b/0x1f0
    [<00000000f7bb938e>] do_syscall_64+0x3b/0x90
    [<000000003fcd67a9>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: c68401011522 ("xfs: expose errortag knobs via sysfs")
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>