mailbox: sprd: correct definition of SPRD_OUTBOX_FIFO_FULL

According to the specification, bit[2] represents SPRD_OUTBOX_FIFO_FULL,
not bit[0], so correct it.

Fixes: ca27fc2 ("mailbox: sprd: Add Spreadtrum mailbox driver")
Signed-off-by: Magnum Shan <magnum.shan@unisoc.com>
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Reviewed-by: Baolin Wang <baolin.wang7@gmail.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/sprd-mailbox.c

@@ -35,7 +35,7 @@
 #define SPRD_MBOX_IRQ_CLR			BIT(0)
 
 /* Bit and mask definiation for outbox's SPRD_MBOX_FIFO_STS register */
-#define SPRD_OUTBOX_FIFO_FULL			BIT(0)
+#define SPRD_OUTBOX_FIFO_FULL			BIT(2)
 #define SPRD_OUTBOX_FIFO_WR_SHIFT		16
 #define SPRD_OUTBOX_FIFO_RD_SHIFT		24
 #define SPRD_OUTBOX_FIFO_POS_MASK		GENMASK(7, 0)