xfs: return a failure address from xfs_rmap_irec_offset_unpack

xfs: return a failure address from xfs_rmap_irec_offset_unpack

Source kernel commit: 39ab26d59f039c6190bbaa8118a8f0ffed84492a

Currently, xfs_rmap_irec_offset_unpack returns only 0 or -EFSCORRUPTED.
Change this function to return the code address of a failed conversion
in preparation for the next patch, which standardizes localized record
checking and reporting code.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>