tools: kwboot: Do not change received character in kwboot_xm_recv_reply()

Marvell BootROM expects retransmission of previous xmodem packet only in
the case when it sends NAK response to the host.

Do not change non-xmodem response (possibly UART transfer error) to NAK
in kwboot_xm_recv_reply() function. Allow caller to receive original
response from device.

Change argument 'nak_on_non_xm' to 'stop_on_non_xm'. Instead of changing
non-xmodem character to NAK, stop processing on invalid character and
return it.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/tools/kwboot.c b/tools/kwboot.c
index 0b97990..a619a6c 100644
--- a/tools/kwboot.c
+++ b/tools/kwboot.c
@@ -875,7 +875,7 @@
 }
 
 static int
-kwboot_xm_recv_reply(int fd, char *c, int nak_on_non_xm,
+kwboot_xm_recv_reply(int fd, char *c, int stop_on_non_xm,
 		     int ignore_nak_reply,
 		     int allow_non_xm, int *non_xm_print,
 		     int baudrate, int *baud_changed)
@@ -931,10 +931,8 @@
 				*non_xm_print = 1;
 			}
 		} else {
-			if (nak_on_non_xm) {
-				*c = NAK;
+			if (stop_on_non_xm)
 				break;
-			}
 			timeout = recv_until - _now();
 			if (timeout < 0) {
 				errno = ETIMEDOUT;