drm/i915: Drop const qualifiers from params in wait_for_register()

drm/i915: Drop const qualifiers from params in wait_for_register()

These params are passed by value, const qualifiers are ignored any way.
While around, unify timeout_ms type from long to int.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Suggested-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170410093817.151280-1-michal.wajdeczko@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>