Forward I2C transfers to the correct device when falling back to GPIO bitbanging.

[jhb]

Summary

It seems certain Intel GPUs use GPIO bitbanging over a child device
instead of GMBUS access for I2C transfers. The GMBUS driver falls back
to this mode when a transfer times out. However, the first transfer to
timeout was sending the request back to itself resulting in an panic due
to recursing on a lock. Fix it to forward the request on to the proper
device. This appears to have been accidentally changed in r277487.

Test Plan

• Try to use drm on an affected GPU. Was tested by Joe Maloney <[e-mail]> in a thread on current@.