serial: fix UART_IIR_ID

UART IRQ Identification bitfield is 3
bits long (bits 3:1) but current mask only
masks 2 bits. Fix it.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 file changed