drivers: misc: ad525x_dpot: Add missing check in dpot_read_spi

The use of dpot_read_r8d8() after checking dpot->uid is similar.
However, we check the return value and return an error code only
in one path, which is odd.

Link: https://lore.kernel.org/r/20210301125057.28819-1-dinghao.liu@zju.edu.cn
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/ad525x_dpot.c

@@ -139,6 +139,9 @@ static s32 dpot_read_spi(struct dpot_data *dpot, u8 reg)
 			value = dpot_read_r8d8(dpot,
 				DPOT_AD5291_READ_RDAC << 2);
 
+			if (value < 0)
+				return value;
+
 			if (dpot->uid == DPOT_UID(AD5291_ID))
 				value = value >> 2;