Fix the active gasmix detection

The Cressi Edy appears to set the disabled gas mixes to 0xFF. The check
for the magic value 0xF0 doesn't catch this case and therefore the value
0xFF results in a gas mix with 165% O2, which is obviously invalid.

Fixed by checking the high nibble only.

Author: jefdriesen

src/cressi_edy_parser.c

@@ -65,7 +65,7 @@ cressi_edy_parser_count_gasmixes (const unsigned char *data)
 	// as the first gas marked as disabled is found.
 	unsigned int i = 0;
 	while (i < 3) {
-		if (data[0x17 - i] == 0xF0)
+		if ((data[0x17 - i] & 0xF0) == 0xF0)
 			break;
 		i++;
 	}