s390/zcrypt: remove incorrect kernel doc indicators

Many comments above functions start with a kernel doc indicator, but
the comments are not using kernel doc style. Get rid of the warnings
by simply removing the indicator.

E.g.:

drivers/s390/crypto/zcrypt_msgtype6.c:111: warning:
 This comment starts with '/**', but isn't a kernel-doc comment.

Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>