[S390] dasd: Avoid compile warnings on !CONFIG_DASD_PROFILE

drivers/s390/block/dasd_proc.c:33:
 warning: 'dasd_get_user_string' defined but not used
drivers/s390/block/dasd_proc.c:172:
 warning: 'dasd_statistics_array' defined but not used

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>