imx: drop warning: unused variable 'max_freq'

max_freq in print_cpuinfo is used only with
imx6.

Signed-off-by: Stefano Babic <sbabic@denx.de>
diff --git a/arch/arm/imx-common/cpu.c b/arch/arm/imx-common/cpu.c
index 275befd..5e56cfe 100644
--- a/arch/arm/imx-common/cpu.c
+++ b/arch/arm/imx-common/cpu.c
@@ -145,7 +145,8 @@
 
 int print_cpuinfo(void)
 {
-	u32 cpurev, max_freq;
+	u32 cpurev;
+	__maybe_unused u32 max_freq;
 
 #if defined(CONFIG_MX6) && defined(CONFIG_IMX6_THERMAL)
 	struct udevice *thermal_dev;