serial: sh-sci: sci_poll_get_char() is only used by CONFIG_CONSOLE_POLL.

sci_poll_put_char() happens to also be used by the serial console,
while sci_poll_get_char() is only used by CONFIG_CONSOLE_POLL. Add
another gnarly ifdef to shut up the compiler.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>