Input: cros_ec_keyb - remove extraneous 'const'

gcc-7 warns about 'const SIMPLE_DEV_PM_OPS', as that macro already contains
a 'const' keyword:

drivers/input/keyboard/cros_ec_keyb.c:663:14: error: duplicate 'const' declaration specifier [-Werror=duplicate-decl-specifier]
 static const SIMPLE_DEV_PM_OPS(cros_ec_keyb_pm_ops, NULL, cros_ec_keyb_resume);

This removes the extra one.

Fixes: 6af6dc2d

 ("input: Add ChromeOS EC keyboard driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>