xfs: remove unnecessary null check in xfs_generic_create

The function posix_acl_release() test the passed-in argument and
move on only when it is non-null, so maybe the null check in
xfs_generic_create is unnecessary.

Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>