drm/i915: Fix kerneldoc for i915_gem_shrink_all

I've botched this, so let's fix it.

Botched in

commit eb0b44ad
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Mar 18 14:47:59 2015 +0100

    drm/i915: kerneldoc for i915_gem_shrinker.c

v2: Be a good citizen^Wmaintainer and add the proper commit citation.
Noticed by Jani.
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/i915/i915_gem_shrinker.c

@@ -143,7 +143,7 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 }
 
 /**
- * i915_gem_shrink - Shrink buffer object caches completely
+ * i915_gem_shrink_all - Shrink buffer object caches completely
  * @dev_priv: i915 device
  *
  * This is a simple wraper around i915_gem_shrink() to aggressively shrink all