serial/arc: Fix warning with CONSOLE_POLL

| drivers/tty/serial/arc_uart.c:516:2: warning: (near initialization for 'arc_serial_pops.poll_put_char') [enabled by default]

This partially undoes "serial/arc: use uart_console_write() helper" by
restoring the prototpye of poll helper and use a different one in
uart_console_write()

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>