serial: sh-sci: Don't set SCLSR bits in the SCxSR error mask

error_mask is the union of all error indicating bits in the SCxSR
register, while overrun_mask may apply to a different register (SCLSR),
depending on the SCI variant.

Hence overrun_mask should only be ORed into error_mask if it applies to
the SCxSR register.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>