serial: sh-sci: Move overrun_bit and error_mask fields out of pdata

None of the fields is ever set by board code, and both of them are set
in the driver at probe time. Move them out of struct plat_sci_port to
struct sci_port.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>