[S390] tape block: fix dependencies

  CC      drivers/s390/char/tape_block.o
In file included from drivers/s390/char/tape_block.c:24:
drivers/s390/char/tape.h:159: warning: 'struct request' declared inside
parameter list

Adding the dependency of CONFIG_BLOCK to CONFIG_S390_TAPE_BLOCK.

Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>