drm/i915: Clean up ancient doc comments for i915_ioc32.c

As befitting a file dedicated to the mistakes of the past,

drivers/gpu/drm/i915/i915_ioc32.c:2: warning: Cannot understand  * \file i915_ioc32.c
 on line 2 - I thought it was a doc line
drivers/gpu/drm/i915/i915_ioc32.c:82: warning: Function parameter or member 'filp' not described in 'i915_compat_ioctl'
drivers/gpu/drm/i915/i915_ioc32.c:82: warning: Function parameter or member 'cmd' not described in 'i915_compat_ioctl'
drivers/gpu/drm/i915/i915_ioc32.c:82: warning: Function parameter or member 'arg' not described in 'i915_compat_ioctl'

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180214160720.19673-1-chris@chris-wilson.co.uk