base-files: fix error message during boot

preinit spews out this message

"cat: can't open '/proc/device-tree/model': No such file or directory"

Signed-off-by: John Crispin <john@phrozen.org>

package/base-files/files/lib/preinit/10_sysinfo

@@ -3,7 +3,7 @@ do_sysinfo_generic() {
 	mkdir -p /tmp/sysinfo
 	[ -e /tmp/sysinfo/board_name ] || \
 		echo "$(strings /proc/device-tree/compatible | head -1)" > /tmp/sysinfo/board_name
-	[ -e /tmp/sysinfo/model ] || \
+	[ -n /tmp/sysinfo/model -a -e /proc/device-tree/model ] && \
 		echo "$(cat /proc/device-tree/model)" > /tmp/sysinfo/model
 }