[media] fmdrv: better define fmdbg() macro to avoid warnings

drivers/media/radio/wl128x/fmdrv_common.c:1619:47: warning: suggest braces around empty body in an 'else' statement [-Wempty-body]
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/radio/wl128x/fmdrv.h

@@ -60,7 +60,7 @@
 #define fmdbg(format, ...) \
 	printk(KERN_DEBUG "fmdrv: " format, ## __VA_ARGS__)
 #else /* DEBUG */
-#define fmdbg(format, ...)
+#define fmdbg(format, ...) do {} while(0)
 #endif
 enum {
 	FM_MODE_OFF,