ion: dummy driver: use ARRAY_SIZE for nr of heaps

use ARRAY_SIZE to count number of heaps in static array
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion_dummy_driver.c

@@ -58,7 +58,7 @@ struct ion_platform_heap dummy_heaps[] = {
 };
 
 struct ion_platform_data dummy_ion_pdata = {
-	.nr = 4,
+	.nr = ARRAY_SIZE(dummy_heaps),
 	.heaps = dummy_heaps,
 };