HID: broken force feedback support for ACRUX gamepad

The force feedback support for the ACRUX gamepad is broken since
2.6.38.8 and more recent kernels due to this
commit:	0ae43810976bc969ee158510c4acbe70ed136e61
The problem is simply with drivers/hid/Kconfig:
HID_ACRUX_FF should be a bool not a tristate. Otherwise the support
for the force feedback is not compiled into the module hid-axff.