media: atomisp: don't cause a warn if probe failed

When probe fails, it is possible that hmm_init() to not be
called. On such case, hmm_cleanup() will cause a WARN_ON().

Avoid it by adding an explicit check at hmm_cleanup() to
ensure that the hmm code was properly initialized.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/staging/media/atomisp/pci/hmm/hmm.c

@@ -208,6 +208,8 @@ int hmm_init(void)
 
 void hmm_cleanup(void)
 {
+	if (!dummy_ptr)
+		return;
 	sysfs_remove_group(&atomisp_dev->kobj, atomisp_attribute_group);
 
 	/* free dummy memory first */