ubi: fastmap: Clean up the initialization of pointer p

The pointer p is being initialized with one value and a few lines
later being set to a newer replacement value. Clean up the code by
using the latter assignment to p as the initial value. Cleans up
clang warning:

drivers/mtd/ubi/fastmap.c:217:19: warning: Value stored to 'p'
during its initialization is never read
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/fastmap.c

@@ -214,9 +214,8 @@ static void assign_aeb_to_av(struct ubi_attach_info *ai,
 			     struct ubi_ainf_volume *av)
 {
 	struct ubi_ainf_peb *tmp_aeb;
-	struct rb_node **p = &ai->volumes.rb_node, *parent = NULL;
+	struct rb_node **p = &av->root.rb_node, *parent = NULL;
 
-	p = &av->root.rb_node;
 	while (*p) {
 		parent = *p;