zram: remove KMSG_COMPONENT macro

The KMSG_COMPONENT macro is a leftover of the s390 specific "kernel
message catalog" from 2008 [1] which never made it upstream.

The macro was added to s390 code to allow for an out-of-tree patch which
used this to generate unique message ids.  Also this out-of-tree doesn't
exist anymore.

The pattern of how the KMSG_COMPONENT is used was partially also used for
non s390 specific code, for whatever reasons.

Remove the macro in order to get rid of a pointless indirection.

Link: https://lkml.kernel.org/r/20251126143602.2207435-1-hca@linux.ibm.com
Link: https://lwn.net/Articles/292650/

 [1]
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>