Fix this compile error:

In file included from drivers/s390/char/tape_core.c:29:0:
drivers/s390/char/tape_std.h:103:66: warning: ‘struct request’ declared inside parameter list [enabled by default]
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>