Adding function to calculate difference between two addresses.

Change-Id: If64d4b5f342f063dd0394c7bcc8a2389a63fe702
diff --git a/src/load.c b/src/load.c
index 66b7034..ef033a6 100644
--- a/src/load.c
+++ b/src/load.c
@@ -180,7 +180,7 @@
 	 */
 	for (i = 0; i < mem_ranges_count; ++i) {
 		if (size_to_find <=
-		    pa_addr(mem_ranges[i].end) - pa_addr(mem_ranges[i].begin)) {
+		    pa_difference(mem_ranges[i].begin, mem_ranges[i].end)) {
 			/*
 			 * This range is big enough, take some of it from the
 			 * end and reduce its size accordingly.