fix(st-clock): avoid arithmetics on pointers

This corrects MISRA C2012-18.4:
The +, -, += and -= operators should not be applied to an expression
of pointer type.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I9128f567a7c83d8e3381428b07e6bd785be2703b
diff --git a/drivers/st/clk/clk-stm32mp13.c b/drivers/st/clk/clk-stm32mp13.c
index faccfd4..db427ad 100644
--- a/drivers/st/clk/clk-stm32mp13.c
+++ b/drivers/st/clk/clk-stm32mp13.c
@@ -2242,7 +2242,7 @@
 	size_t i = 0U;
 
 	for (i = _PLL1; i < pdata->npll; i++) {
-		struct stm32_pll_dt_cfg *pll = pdata->pll + i;
+		struct stm32_pll_dt_cfg *pll = &pdata->pll[i];
 		char name[RCC_PLL_NAME_SIZE];
 		int subnode = 0;
 		int err = 0;