Fix build errors when I2C=m and SURFACE_3_BUTTON=y.
The driver uses i2c interfaces so it should depend on I2C.

drivers/built-in.o: In function `surface3_driver_init':
surface3_button.c:(.init.text+0x75cb0): undefined reference to `i2c_register_driver'
drivers/built-in.o: In function `surface3_driver_exit':
surface3_button.c:(.exit.text+0x31a8): undefined reference to `i2c_del_driver'

Fixes: 1a64b719 (platform/x86: Introduce button support for the Surface 3)
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Cc: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Cc: platform-driver-x86@vger.kernel.org
Cc: Darren Hart <dvhart@infradead.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>