drm/i915: Update i915_reset parameter for kerneldoc

Since commit c033666a

 ("drm/i915: Store a i915 backpointer from
engine, and use it") i915_reset receives dev_priv, but the kerneldoc
was not updated.

Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170112041817.1102-3-michel.thierry@intel.com