s390/raw3270: improve raw3270_init() readability

Instead of checking if rc is 0, check whether it is non-zero and return
early if so. The call to class_create() can fail, so add a check to it and
move it out of the mutex region.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Ricardo B. Marliere" <ricardo@marliere.net>
Link: https://lore.kernel.org/r/20240305-class_cleanup-s390-v1-5-c4ff1ec49ffd@marliere.net


Signed-off-by: Heiko Carstens <hca@linux.ibm.com>