command: Prefer uint8_t* for buffers; prefer uint8_fast_t for lengths

Prefer using 'uint8_t' buffers as it is too easy to run into C sign
extension problems with 'char' buffers.  Prefer using 'uint_fast8_t'
for buffer lengths as gcc does a better job compiling them on 32bit
mcus.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/generic/misc.h

@@ -16,6 +16,6 @@ void timer_kick(void);
 void *dynmem_start(void);
 void *dynmem_end(void);
 
-uint16_t crc16_ccitt(char *buf, uint8_t len);
+uint16_t crc16_ccitt(uint8_t *buf, uint_fast8_t len);
 
 #endif // misc.h