serial: sh-sci: Call sci_serial_{in,out}() directly

Unlike the 8250 serial driver complex, the sh-sci driver uses only a
single pair of functions to read and write serial port registers.
Hence there is no need to incur the overhead of calling them through
indirection, like the serial_port_{in,out}() wrappers do.

Replace all calls to these wrappers by direct calls to
sci_serial_{in,out}().

Remove the setup of the uart_port.serial_{in,out}() callbacks.  After
removal of all calls to serial_port_{in,out}() in the sh-sci driver, the
only remaining user is uart_xchar_out(), which the sh-sci driver does
not use.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/51e79d601cb9d9d63822d3773d3cf05a96868612.1709548811.git.geert+renesas@glider.be
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>