sh-sci: update receive error handling for muxed irqs

This patch updates the receive error code for muxed
interrupts in the sh-sci driver.

Receive error interrupts may be generated by the hardware
if RE or REIE bits in SCSCR are set. Update the muxed
interrupt handling code to acknowledge error interrupts
if RE or REIE is set, instead of only acknowledging if
REIE is set.

Without this patch error interrupts may be generated but
never acked resulting in a "nobody cared" crash.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>