Tidy clang build warnings

- Remove transceiver enums from hackrf.h
 - convert uint64_ts to int64_ts for frequency maths

host/libhackrf/src/hackrf.h

@@ -82,14 +82,6 @@ enum rf_path_filter {
 	RF_PATH_FILTER_HIGH_PASS = 2,
 };
 
-typedef enum {
-	TRANSCEIVER_MODE_OFF = 0,
-	TRANSCEIVER_MODE_RX = 1,
-	TRANSCEIVER_MODE_TX = 2,
-	TRANSCEIVER_MODE_SS = 3,
-	TRANSCEIVER_MODE_CPLD_UPDATE = 4
-} transceiver_mode_t;
-
 typedef struct hackrf_device hackrf_device;
 
 typedef struct {