leds: blinkm: avoid uninitialized data use

gcc-8 reports missing error handling in blinkm_detect, when blinkm()
fails, tmpargs[] is uninitialized:

drivers/leds/leds-blinkm.c: In function 'blinkm_detect':
drivers/leds/leds-blinkm.c:555:6: error: 'tmpargs' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This adds a missing error checks.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NJacek Anaszewski <jacek.anaszewski@gmail.com>

drivers/leds/leds-blinkm.c

@@ -549,8 +549,12 @@ static int blinkm_detect(struct i2c_client *client, struct i2c_board_info *info)
 	/* make sure the blinkM is balanced (read/writes) */
 	while (count > 0) {
 		ret = blinkm_write(client, BLM_GET_ADDR, NULL);
+		if (ret)
+			return ret;
 		usleep_range(5000, 10000);
 		ret = blinkm_read(client, BLM_GET_ADDR, tmpargs);
+		if (ret)
+			return ret;
 		usleep_range(5000, 10000);
 		if (tmpargs[0] == 0x09)
 			count = 0;