imx8mn: buffer overflow in low_drive_gpu_freq()

Avoid a buffer overflow if assigned-clock-rates has less than two elements.

Fixes: 98bcdf16356c ("imx8mn: Add low drive mode support for DDR4/LPDDR4 EVK")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/imx8m/soc.c b/arch/arm/mach-imx/imx8m/soc.c
index df865e9..20672de 100644
--- a/arch/arm/mach-imx/imx8m/soc.c
+++ b/arch/arm/mach-imx/imx8m/soc.c
@@ -914,6 +914,8 @@
 
 	if (cnt != 7)
 		printf("Warning: %s, assigned-clock-rates count %d\n", nodes_path_8mn[0], cnt);
+	if (cnt < 2)
+		return -1;
 
 	assignedclks[cnt - 1] = 200000000;
 	assignedclks[cnt - 2] = 200000000;