xfs: Fix default ASSERT in xfs_attr_set_iter

xfs: Fix default ASSERT in xfs_attr_set_iter

Source kernel commit: 4a4957c16dc674d1306a3b43d6b07ed93a7b7a14

This ASSERT checks for the state value of RM_SHRINK in the set path
which should never happen.  Change to ASSERT(0);

Suggested-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>