drm/i915: Clear ret before unbinding in i915_gem_evict_something()

Missed when rebasing patches, I failed to set ret to zero before
starting the unbind loop (which depends upon ret being zero).

Reported-by: Matthew Auld <[e-mail]>
Fixes: 9332f3b1b99a ("drm/i915: Combine loops within i915_gem_evict_something")
Signed-off-by: Chris Wilson <[e-mail]>
Cc: Matthew Auld <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]
Reviewed-by: Matthew Auld <[e-mail]>
Cc: <[e-mail]> # v4.9+
(cherry picked from commit 121dfbb2a2ef1c5f49e15c38ccc47ff0beb59446)
Signed-off-by: Jani Nikula <[e-mail]>

drivers/gpu/drm/i915/i915_gem_evict.c

···
 	}
 
 	/* Unbinding will emit any required flushes */
+	ret = 0;
 	while (!list_empty(&eviction_list)) {
 		vma = list_first_entry(&eviction_list,
 				       struct i915_vma,