CHROMIUM: platform/x86 - fix compiler warning for args of bus_find_devices

CHROMIUM: platform/x86 - fix compiler warning for args of bus_find_devices

bus_find_devices() expects a non-const void * for its 3rd argument.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
BUG=chromium-os:27714,chrome-os-partner:8547
TEST=builds clean (without the following warning):
  drivers/platform/x86/chromeos_laptop.c: In function 'find_i2c_adapter_num':
  drivers/platform/x86/chromeos_laptop.c:193:10: warning: passing argument 3 of 'bus_find_device' discards 'const' qualifier from pointer target type [enabled by default]
  include/linux/device.h:118:16: note: expected 'void *' but argument is of type 'char const *'

Change-Id: I24ee960408c0736f75a40c21598eed4ab1e5550a
Reviewed-on: https://gerrit.chromium.org/gerrit/18465
Commit-Ready: Benson Leung <bleung@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Tested-by: Benson Leung <bleung@chromium.org>