xfs: simplify returns in xchk_bmap

Remove the pointless goto and return code in xchk_bmap, since it only
serves to obscure what's going on in the function.  Instead, return
whichever error code is appropriate there.  For nonexistent forks,
this should have been ENOENT.

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