xfs: kill __KERNEL__ check for debug code in allocation code

Userspace running debug builds is relatively rare, so there's need
to special case the allocation algorithm code coverage debug switch.
As it is, userspace defines random numbers to 0, so  invert the
logic of the switch so it is effectively a no-op in userspace.
This kills another couple of __KERNEL__ users.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>