uart: 16550: Fix getc

tbz check for RDR status is to check for a bit being zero.
Unfortunately, we are using a mask rather than the bit position.

Further as per http://www.ti.com/lit/ds/symlink/pc16550d.pdf (page 17),
LSR register bit 0 is Data ready status (RDR), not bit position 2.

Update the same to match the specification.

Reported-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
diff --git a/drivers/ti/uart/aarch64/16550_console.S b/drivers/ti/uart/aarch64/16550_console.S
index 0535381..8466482 100644
--- a/drivers/ti/uart/aarch64/16550_console.S
+++ b/drivers/ti/uart/aarch64/16550_console.S
@@ -146,7 +146,7 @@
 func console_core_getc
 	/* Check if the receive FIFO is empty */
 1:	ldr	w1, [x0, #UARTLSR]
-	tbz	w1, #UARTLSR_RDR, 1b
+	tbz	w1, #UARTLSR_RDR_BIT, 1b
 	ldr	w0, [x0, #UARTRX]
 	ret
 getc_error: