drm/i915/selftests: Fix return in assert_mmap_offset()

The assert_mmap_offset() returns type bool so if we return an error
pointer that is "return true;" or success.  If we have an error, then
we should return false.

Fixes: 3d81d589 ("drm/i915: Test exhaustion of the mmap space")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200228141413.qfjf4abr323drlo4@kili.mountain
(cherry picked from commit efbf9288)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c

@@ -570,7 +570,7 @@ static bool assert_mmap_offset(struct drm_i915_private *i915,
 
 	obj = i915_gem_object_create_internal(i915, size);
 	if (IS_ERR(obj))
-		return PTR_ERR(obj);
+		return false;
 
 	mmo = mmap_offset_attach(obj, I915_MMAP_OFFSET_GTT, NULL);
 	i915_gem_object_put(obj);