cosmetic: Fix "implicit fall-through" gcc 7.3.0 warnings

src/convenience/convenience.c

@@ -49,9 +49,11 @@ double atofs(char *s)
 		case 'g':
 		case 'G':
 			suff *= 1e3;
+			/* fall-through */
 		case 'm':
 		case 'M':
 			suff *= 1e3;
+			/* fall-through */
 		case 'k':
 		case 'K':
 			suff *= 1e3;
@@ -76,9 +78,11 @@ double atoft(char *s)
 		case 'h':
 		case 'H':
 			suff *= 60;
+			/* fall-through */
 		case 'm':
 		case 'M':
 			suff *= 60;
+			/* fall-through */
 		case 's':
 		case 'S':
 			suff *= atof(s);

src/librtlsdr.c

@@ -1594,6 +1594,7 @@ found:
 	switch (dev->tuner_type) {
 	case RTLSDR_TUNER_R828D:
 		dev->tun_xtal = R828D_XTAL_FREQ;
+		/* fall-through */
 	case RTLSDR_TUNER_R820T:
 		/* disable Zero-IF mode */
 		rtlsdr_demod_write_reg(dev, 1, 0xb1, 0x1a, 1);

src/rtl_eeprom.c

@@ -303,6 +303,7 @@ int main(int argc, char **argv)
 		case 'w':
 			flash_file = 1;
 			change = 1;
+			/* fall-through */
 		case 'r':
 			filename = optarg;
 			break;