of: reserved-memory: Fix using wrong number of cells to get property 'alignment'

According to DT spec, size of property 'alignment' is based on parent
node’s #size-cells property.

But __reserved_mem_alloc_size() wrongly uses @dt_root_addr_cells to get
the property obviously.

Fix by using @dt_root_size_cells instead of @dt_root_addr_cells.

Fixes: 3f0c820 ("drivers: of: add initialization code for dynamic reserved memory")
Cc: stable@vger.kernel.org
Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Link: https://lore.kernel.org/r/20250109-of_core_fix-v4-9-db8a72415b8c@quicinc.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Author: zijun-hu

drivers/of/of_reserved_mem.c

@@ -409,12 +409,12 @@ static int __init __reserved_mem_alloc_size(unsigned long node, const char *unam
 
 	prop = of_get_flat_dt_prop(node, "alignment", &len);
 	if (prop) {
-		if (len != dt_root_addr_cells * sizeof(__be32)) {
+		if (len != dt_root_size_cells * sizeof(__be32)) {
 			pr_err("invalid alignment property in '%s' node.\n",
 				uname);
 			return -EINVAL;
 		}
-		align = dt_mem_next_cell(dt_root_addr_cells, &prop);
+		align = dt_mem_next_cell(dt_root_size_cells, &prop);
 	}
 
 	nomap = of_get_flat_dt_prop(node, "no-map", NULL) != NULL;