autocore: display ? if "model name" doesn't exist

Signed-off-by: CN_SZTL <cnsztl@project-openwrt.eu.org>
(cherry-pick from 285bb05ca3)

package/lean/autocore/files/arm/sbin/cpuinfo

@@ -1,6 +1,7 @@
 #!/bin/sh
 
 cpu_arch="$(cat "/proc/cpuinfo" | grep "model name" | sed -n "1p" | awk -F ': ' '{print $2}')"
+[ -z "${cpu_arch}" ] && cpu_arch="?"
 cpu_cores="$(cat "/proc/cpuinfo" | grep "processor" | wc -l)"
 
 if grep -q "bcm27xx" "/etc/openwrt_release"; then