drm/bridge: nxp-ptn3460: fix i2c_master_send() error checking

The i2c_master_send/recv() functions return negative error codes or the
number of bytes that were able to be sent/received.  This code has
two problems.  1)  Instead of checking if all the bytes were sent or
received, it checks that at least one byte was sent or received.
2) If there was a partial send/receive then we should return a negative
error code but this code returns success.

Fixes: a9fe713d ("drm/bridge: Add PTN3460 bridge driver")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/0cdc2dce-ca89-451a-9774-1482ab2f4762@moroto.mountain

drivers/gpu/drm/bridge/nxp-ptn3460.c

@@ -56,13 +56,13 @@ static int ptn3460_read_bytes(struct ptn3460_bridge *ptn_bridge, char addr,
 	ret = i2c_master_send(ptn_bridge->client, &addr, 1);
 	if (ret <= 0) {
 		DRM_ERROR("Failed to send i2c command, ret=%d\n", ret);
-		return ret;
+		return ret ?: -EIO;
 	}
 
 	ret = i2c_master_recv(ptn_bridge->client, buf, len);
-	if (ret <= 0) {
+	if (ret != len) {
 		DRM_ERROR("Failed to recv i2c data, ret=%d\n", ret);
-		return ret;
+		return ret < 0 ? ret : -EIO;
 	}
 
 	return 0;
@@ -78,9 +78,9 @@ static int ptn3460_write_byte(struct ptn3460_bridge *ptn_bridge, char addr,
 	buf[1] = val;
 
 	ret = i2c_master_send(ptn_bridge->client, buf, ARRAY_SIZE(buf));
-	if (ret <= 0) {
+	if (ret != ARRAY_SIZE(buf)) {
 		DRM_ERROR("Failed to send i2c command, ret=%d\n", ret);
-		return ret;
+		return ret < 0 ? ret : -EIO;
 	}
 
 	return 0;