dfu: remove limitation on partition size

Change long (32 bits on arm) to u64 (same type than offset)
for size and read offset r_left

So partition and device used for DFU can be greater than 4GB

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/drivers/dfu/dfu_nand.c b/drivers/dfu/dfu_nand.c
index ed4ceb7..6dc9ff7 100644
--- a/drivers/dfu/dfu_nand.c
+++ b/drivers/dfu/dfu_nand.c
@@ -114,7 +114,7 @@
 	return ret;
 }
 
-int dfu_get_medium_size_nand(struct dfu_entity *dfu, long *size)
+int dfu_get_medium_size_nand(struct dfu_entity *dfu, u64 *size)
 {
 	*size = dfu->data.nand.size;