iio: trigger: stm32-timer: fix get trigger mode

Fix reading trigger mode, when other bit-fields are set. SMCR register
value must be masked to read SMS (slave mode selection) only.

Fixes: 9eba381b ("iio: make stm32 trigger driver use
INDIO_HARDWARE_TRIGGERED mode")
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/trigger/stm32-timer-trigger.c

@@ -485,7 +485,7 @@ static int stm32_get_trigger_mode(struct iio_dev *indio_dev,
 
 	regmap_read(priv->regmap, TIM_SMCR, &smcr);
 
-	return smcr == TIM_SMCR_SMS ? 0 : -EINVAL;
+	return (smcr & TIM_SMCR_SMS) == TIM_SMCR_SMS ? 0 : -EINVAL;
 }
 
 static const struct iio_enum stm32_trigger_mode_enum = {