tests: Make realloc_fdt() really allocate *fdt

This bug has been found by using clang Static Analyzer: it reported that
the value stored to fdt was never read.

Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/sw_tree1.c

@@ -42,14 +42,14 @@ static void realloc_fdt(void **fdt, size_t *size, bool created)
 	switch (alloc_mode) {
 	case FIXED:
 		if (!(*fdt))
-			fdt = xmalloc(*size);
+			*fdt = xmalloc(*size);
 		else
 			FAIL("Ran out of space");
 		return;
 
 	case RESIZE:
 		if (!(*fdt)) {
-			fdt = xmalloc(SPACE);
+			*fdt = xmalloc(SPACE);
 		} else if (*size < SPACE) {
 			*size += 1;
 			fdt_resize(*fdt, *fdt, *size);