block: rsxx: select CONFIG_CRC32

Without crc32, the driver fails to link:

arm-linux-gnueabi-ld: drivers/block/rsxx/config.o: in function `rsxx_load_config':
config.c:(.text+0x124): undefined reference to `crc32_le'

Fixes: 8722ff8c ("block: IBM RamSan 70/80 device driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>