staging: android: ion: set init function as static

Fix warning issued by sparse:
symbol 'ion_device_create' was not declared. Should it be static?
Signed-off-by: Paolo Cretaro <melko@frugalware.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion.c

@@ -586,7 +586,7 @@ void ion_device_add_heap(struct ion_heap *heap)
 }
 EXPORT_SYMBOL(ion_device_add_heap);
 
-int ion_device_create(void)
+static int ion_device_create(void)
 {
 	struct ion_device *idev;
 	int ret;