i2c: rk3x: fix 0 length write transfers

i2cdetect -q was broken (everything was a false positive, and no transfers were
actually being sent over i2c). The way it works is by sending a 0 length write
request and checking for NACK. This patch fixes the 0 length writes and actually
sends them.

Reported-by: Doug Anderson <[e-mail]>
Signed-off-by: Alexandru M Stan <[e-mail]>
Tested-by: Doug Anderson <[e-mail]>
Tested-by: Max Schwarz <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>
Cc: [e-mail]

drivers/i2c/busses/i2c-rk3x.c

···
 	for (i = 0; i < 8; ++i) {
 		val = 0;
 		for (j = 0; j < 4; ++j) {
-			if (i2c->processed == i2c->msg->len)
+			if ((i2c->processed == i2c->msg->len) && (cnt != 0))
 				break;
 
 			if (i2c->processed == 0 && cnt == 0)