input: cros_ec_keyb_clear_keyboard() depends on CONFIG_PM_SLEEP

If CONFIG_PM_SLEEP is not set:

drivers/input/keyboard/cros_ec_keyb.c:211: warning: ‘cros_ec_keyb_clear_keyboard’ defined but not used

Move the definition of cros_ec_keyb_clear_keyboard() inside the section
protected by #ifdef CONFIG_PM_SLEEP to fix this.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>