drm/msm/dp: replace variable err with len at dp_aux_link_power_up()

drm_dp_dpcd_readb() will return 1 to indicate one byte had been read
successfully. This patch replace variable "err" with "len" have more
correct meaning.

changes in v5:
-- split into 3 patches

Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/502533/
Link: https://lore.kernel.org/r/1662999830-13916-3-git-send-email-quic_khsieh@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

Author: Kuogee Hsieh

drivers/gpu/drm/msm/dp/dp_link.c

@@ -49,21 +49,21 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
 					struct dp_link_info *link)
 {
 	u8 value;
-	int err;
+	ssize_t len;
 
 	if (link->revision < 0x11)
 		return 0;
 
-	err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
-	if (err < 0)
-		return err;
+	len = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
+	if (len < 0)
+		return len;
 
 	value &= ~DP_SET_POWER_MASK;
 	value |= DP_SET_POWER_D0;
 
-	err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
-	if (err < 0)
-		return err;
+	len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
+	if (len < 0)
+		return len;
 
 	usleep_range(1000, 2000);