power: bq27xxx_battery: mark some symbols __maybe_unused

power: bq27xxx_battery: mark some symbols __maybe_unused

Without the I2C driver, we get a few warnings:

drivers/power/bq27xxx_battery.c:288:12: error: 'bq27xxx_regs' defined but not used [-Werror=unused-variable]
 static u8 *bq27xxx_regs[] = {
            ^
drivers/power/bq27xxx_battery.c:994:12: error: 'bq27xxx_powersupply_init' defined but not used [-Werror=unused-function]
 static int bq27xxx_powersupply_init(struct bq27xxx_device_info *di,
            ^
drivers/power/bq27xxx_battery.c:1029:13: error: 'bq27xxx_powersupply_unregister' defined but not used [-Werror=unused-function]
 static void bq27xxx_powersupply_unregister(struct bq27xxx_device_info *di)
             ^

In mainline kernels, this was addressed by a larger rework in 703df6c09795 ("power:
bq27xxx_battery: Reorganize I2C into a module"). We probably don't want this backported
into stable kernels, so instead let's shut up the warnings by marking the symbols
as __maybe_unused.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>