sysmobts: The code allowed a out of bounds access to temp_type_str

The array has three elements but check was for > _NUM_TEMP_TYPES (3)
so an access at array[3] was possible. It is unlikely to have
happened due the usage of enums. Use ARRAY_SIZE and >= on the real
array to avoid this problem.

Fixes: Coverity CID 1040760

src/osmo-bts-sysmo/misc/sysmobts_misc.c

@@ -64,7 +64,7 @@ int sysmobts_temp_get(enum sysmobts_temp_sensor sensor,
 	    sensor > SYSMOBTS_TEMP_RF)
 		return -EINVAL;
 
-	if (type > _NUM_TEMP_TYPES)
+	if (type >= ARRAY_SIZE(temp_type_str))
 		return -EINVAL;
 
 	snprintf(buf, sizeof(buf)-1, TEMP_PATH, sensor, temp_type_str[type]);