drm/msm/dsi: Simplify the code to get the number of read byte

During cmd rx, only new versions of H/W provide register to read back
the real number of byte returned by panel. For the old versions, reading
this register will not get the right number. In fact, we only need to
assume the returned data is the same size as we expected, because later
we will check the data type to detect error.
Signed-off-by: Hai Li <hali@codeaurora.org>

drivers/gpu/drm/msm/dsi/dsi_host.c

@@ -1093,7 +1093,6 @@ static int dsi_cmd_dma_rx(struct msm_dsi_host *msm_host,
 {
 	u32 *lp, *temp, data;
 	int i, j = 0, cnt;
-	bool ack_error = false;
 	u32 read_cnt;
 	u8 reg[16];
 	int repeated_bytes = 0;
@@ -1105,15 +1104,10 @@ static int dsi_cmd_dma_rx(struct msm_dsi_host *msm_host,
 	if (cnt > 4)
 		cnt = 4; /* 4 x 32 bits registers only */
 
-	/* Calculate real read data count */
-	read_cnt = dsi_read(msm_host, 0x1d4) >> 16;
-
-	ack_error = (rx_byte == 4) ?
-		(read_cnt == 8) : /* short pkt + 4-byte error pkt */
-		(read_cnt == (pkt_size + 6 + 4)); /* long pkt+4-byte error pkt*/
-
-	if (ack_error)
-		read_cnt -= 4; /* Remove 4 byte error pkt */
+	if (rx_byte == 4)
+		read_cnt = 4;
+	else
+		read_cnt = pkt_size + 6;
 
 	/*
 	 * In case of multiple reads from the panel, after the first read, there