cmd_nand: fix warning: str2long ncompatible pointer type

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/common/cmd_nand.c b/common/cmd_nand.c
index 1a3c1df..37eb41b 100644
--- a/common/cmd_nand.c
+++ b/common/cmd_nand.c
@@ -110,7 +110,7 @@
 			}
 			*off = part->offset;
 			if (argc >= 2) {
-				if (!(str2long(argv[1], size))) {
+				if (!(str2long(argv[1], (ulong *)size))) {
 					printf("'%s' is not a number\n", argv[1]);
 					return -1;
 				}