HID: hid-sensor-hub: fix duplicate sysfs entry error

Fix kernel warning and failure to register sensor hub devices with MFD.  Now
many devices has in-built sensor hubs. So by default this HID hub, is properly
parsed and register individual sensors as platform device using MFD framework.
But if a second sensor hub is attached via USB, which has same sensors, it will
result in kernel warning and failure to register MFD cell as the platform
device sysfs file name will be same as created by in-built sensor hubs. This
patch sets MFD cell id to PLATFORM_DEVID_AUTO. In this way there will never be
duplicate sysfs file names.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>