xfs: remove flags argument from xchk_setup_xattr_buf

All callers pass XCHK_GFP_FLAGS as the flags argument to
xchk_setup_xattr_buf, so get rid of the argument.

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