backlight: Remove unnecessary and confusing NULL checks

At this point path must point to an allocated string since otherwise the
asprintf that makes the allocation would have failed and we would have
returned earlier.

src/libbacklight.c

@@ -69,7 +69,6 @@ static long backlight_get(struct backlight *backlight, char *node)
 	ret = value;
 out:
 	close(fd);
-	if (path)
 	free(path);
 	return ret;
 }
@@ -127,7 +126,6 @@ long backlight_set_brightness(struct backlight *backlight, long brightness)
 out:
 	if (buffer)
 		free(buffer);
-	if (path)
 	free(path);
 	close(fd);
 	return ret;