serial: amba-pl011: fix incorrect integer size in pl011_fifo_to_tty()

The UART_DUMMY_DR_RX status bit is equal to (1 << 16), so a u16 is too small
to hold that value.  The result is that UART_DUMMY_DR_RX is never passed
to uart_insert_char().  This means that we're always accepting characters,
even when CREAD (in termios) is not set.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>