drm/i915: Free requests after object release when retiring requests

Freeing a request triggers the destruction of the context. This needs to
occur after all objects are themselves unbound from the context, and so
the free request needs to occur after the object release during retire.

This tidies up

commit e2078043
Author: Ben Widawsky <ben@bwidawsk.net>
Date:   Fri Dec 6 14:11:22 2013 -0800

    drm/i915: Defer request freeing

by simply swapping the order of operations rather than introducing
further complexity - as noted during review.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>