lib: crc64: include <linux/crc64.h> for 'crc64_be'

The crc64_be() is declared in <linux/crc64.h> so include
this where the symbol is defined to avoid the following
warning:

lib/crc64.c:43:12: warning: symbol 'crc64_be' was not declared. Should it be static?

Signed-off-by: Ben Dooks (Codethink) <ben.dooks@codethink.co.uk>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>