Fixed minor warning

src/crc64.c

@@ -171,7 +171,7 @@ static const uint64_t crc64_tab[256] = {
 };
 
 
-uint64_t crc64(const unsigned char* s, uint64_t l)
+uint64_t crc64(const char* s, uint64_t l)
 {
 	uint64_t j;
     uint64_t crc = 0;

src/crc64.h

@@ -6,4 +6,4 @@
 
 #include <stdint.h>
 
-uint64_t crc64(const unsigned char* s, uint64_t l);
+uint64_t crc64(const char* s, uint64_t l);