drm/i915/gem: Make drop_pages() return bool

Commit e4e80625 ("drm/i915: Change shrink ordering to use locking
around unbinding.") changed the return type to int without changing the
return values or their meaning to "0 is success". Move it back to
boolean.
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220503061556.513175-1-lucas.demarchi@intel.com

drivers/gpu/drm/i915/gem/i915_gem_shrinker.c

@@ -36,7 +36,7 @@ static bool can_release_pages(struct drm_i915_gem_object *obj)
 	return swap_available() || obj->mm.madv == I915_MADV_DONTNEED;
 }
 
-static int drop_pages(struct drm_i915_gem_object *obj,
+static bool drop_pages(struct drm_i915_gem_object *obj,
 		       unsigned long shrink, bool trylock_vm)
 {
 	unsigned long flags;