drm/bridge/synopsys: dsi: readl_poll_timeout return value clean up

The readl_poll_timeout() return value is 0 in case of success
so it is better to detect errors without taking care of the
return value sign.

Signed-off-by: Philippe Cornu <philippe.cornu@st.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180204213624.18288-1-philippe.cornu@st.com

drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c

@@ -342,7 +342,7 @@ static int dw_mipi_dsi_gen_pkt_hdr_write(struct dw_mipi_dsi *dsi, u32 hdr_val)
 	ret = readl_poll_timeout(dsi->base + DSI_CMD_PKT_STATUS,
 				 val, !(val & GEN_CMD_FULL), 1000,
 				 CMD_PKT_STATUS_TIMEOUT_US);
-	if (ret < 0) {
+	if (ret) {
 		dev_err(dsi->dev, "failed to get available command FIFO\n");
 		return ret;
 	}
@@ -353,7 +353,7 @@ static int dw_mipi_dsi_gen_pkt_hdr_write(struct dw_mipi_dsi *dsi, u32 hdr_val)
 	ret = readl_poll_timeout(dsi->base + DSI_CMD_PKT_STATUS,
 				 val, (val & mask) == mask,
 				 1000, CMD_PKT_STATUS_TIMEOUT_US);
-	if (ret < 0) {
+	if (ret) {
 		dev_err(dsi->dev, "failed to write command FIFO\n");
 		return ret;
 	}
@@ -385,7 +385,7 @@ static int dw_mipi_dsi_write(struct dw_mipi_dsi *dsi,
 		ret = readl_poll_timeout(dsi->base + DSI_CMD_PKT_STATUS,
 					 val, !(val & GEN_PLD_W_FULL), 1000,
 					 CMD_PKT_STATUS_TIMEOUT_US);
-		if (ret < 0) {
+		if (ret) {
 			dev_err(dsi->dev,
 				"failed to get available write payload FIFO\n");
 			return ret;
@@ -721,13 +721,13 @@ static void dw_mipi_dsi_dphy_enable(struct dw_mipi_dsi *dsi)
 
 	ret = readl_poll_timeout(dsi->base + DSI_PHY_STATUS, val,
 				 val & PHY_LOCK, 1000, PHY_STATUS_TIMEOUT_US);
-	if (ret < 0)
+	if (ret)
 		DRM_DEBUG_DRIVER("failed to wait phy lock state\n");
 
 	ret = readl_poll_timeout(dsi->base + DSI_PHY_STATUS,
 				 val, val & PHY_STOP_STATE_CLK_LANE, 1000,
 				 PHY_STATUS_TIMEOUT_US);
-	if (ret < 0)
+	if (ret)
 		DRM_DEBUG_DRIVER("failed to wait phy clk lane stop state\n");
 }