refactor(stm32mp_clk): keep RCC node offset

To avoid parsing device tree file too often, keep the RCC node
offset value in a variable in fdt_get_rcc_node().

Change-Id: Ibb23ff92247d57c65a23517b8f3473f639794d2a
Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/drivers/st/clk/stm32mp_clkfunc.c b/drivers/st/clk/stm32mp_clkfunc.c
index 2101171..d57f120 100644
--- a/drivers/st/clk/stm32mp_clkfunc.c
+++ b/drivers/st/clk/stm32mp_clkfunc.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2020, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2017-2021, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -163,7 +163,13 @@
  */
 static int fdt_get_rcc_node(void *fdt)
 {
-	return fdt_node_offset_by_compatible(fdt, -1, DT_RCC_CLK_COMPAT);
+	static int node;
+
+	if (node <= 0) {
+		node = fdt_node_offset_by_compatible(fdt, -1, DT_RCC_CLK_COMPAT);
+	}
+
+	return node;
 }
 
 /*