mailbox: bcm2708-vcio: Check the correct status register before writing

With the VC reader blocked and the ARM writing, MAIL0_STA reads
empty permanently while MAIL1_STA goes from empty (0x40000000)
to non-empty (0x00000001-0x00000007) to full (0x80000008).

Suggested-by: Phil Elwell <phil@raspberrypi.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>

Author: notro

drivers/mailbox/bcm2708-vcio.c

@@ -35,6 +35,7 @@
 #define MAIL0_STA	0x18	/* status */
 #define MAIL0_CNF	0x1C	/* configuration */
 #define MAIL1_WRT	0x20	/* write - and next 4 words */
+#define MAIL1_STA	0x38	/* status */
 
 /* On MACH_BCM270x these come through <linux/interrupt.h> (arm_control.h ) */
 #ifndef ARM_MS_EMPTY
@@ -85,7 +86,7 @@ static int mbox_write(struct vc_mailbox *mbox, unsigned chan, uint32_t data28)
 		return -EINVAL;
 
 	/* wait for the mailbox FIFO to have some space in it */
-	while (0 != (readl(mbox->regs + MAIL0_STA) & ARM_MS_FULL))
+	while (0 != (readl(mbox->regs + MAIL1_STA) & ARM_MS_FULL))
 		cpu_relax();
 
 	writel(MBOX_MSG(chan, data28), mbox->regs + MAIL1_WRT);