rtlsdr_callback: use correct pointer type for buffer

Silences a clang warning.

Signed-off-by: Steve Markgraf <steve@steve-m.de>

include/rtl-sdr.h

@@ -62,7 +62,7 @@ RTLSDR_API int rtlsdr_reset_buffer(rtlsdr_dev_t *dev);
 
 RTLSDR_API int rtlsdr_read_sync(rtlsdr_dev_t *dev, void *buf, int len, int *n_read);
 
-typedef void(*rtlsdr_async_read_cb_t)(const char *buf, uint32_t len, void *ctx);
+typedef void(*rtlsdr_async_read_cb_t)(unsigned char *buf, uint32_t len, void *ctx);
 
 RTLSDR_API int rtlsdr_wait_async(rtlsdr_dev_t *dev, rtlsdr_async_read_cb_t cb, void *ctx);
 

src/main.c

@@ -48,7 +48,7 @@ static void sighandler(int signum)
 	rtlsdr_cancel_async(dev);
 }
 
-void rtlsdr_callback(const char *buf, uint32_t len, void *ctx)
+void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx)
 {
 	fwrite(buf, len, 1, (FILE*)ctx);
 }