crc32 is uint32_t, not unsigned long

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/crc/crc32.h b/crc/crc32.h
index b7e5eee..d59a560 100644
--- a/crc/crc32.h
+++ b/crc/crc32.h
@@ -18,6 +18,6 @@
 #ifndef CRC32_H
 #define CRC32_H
 
-extern unsigned long crc32(const void * const, unsigned long);
+extern uint32_t crc32(const void * const, unsigned long);
 
 #endif