xtensa: ISS: fix rs_put_char

ISS serial console prints garbage instead of symbols printed via
rs_put_char. gcc optimizes away putting prined symbol into memory buffer
because there's no evidence that the buffer is used afterwards.

Make rs_put_char and rs_write use simc_write that has explicit wmb.

Signed-off-by: Max Filippov <[e-mail]>
Signed-off-by: Chris Zankel <[e-mail]>

arch/xtensa/platforms/iss/console.c

···
 {
 	/* see drivers/char/serialX.c to reference original version */
 
-	__simc (SYS_write, 1, (unsigned long)buf, count, 0, 0);
+	simc_write(1, buf, count);
 	return count;
 }
 
···
 
 static int rs_put_char(struct tty_struct *tty, unsigned char ch)
 {
-	char buf[2];
-
-	buf[0] = ch;
-	buf[1] = '\0';		/* Is this NULL necessary? */
-	__simc (SYS_write, 1, (unsigned long) buf, 1, 0, 0);
-	return 1;
+	return rs_write(tty, &ch, 1);
 }
 
 static void rs_flush_chars(struct tty_struct *tty)