Rockchip family tweaks: add to group only if group doesn't exists yet (#8479)

This way started to fail with Debian Trixie

Co-authored-by: Paolo <paolo.sabatino@gmail.com>

Author: igorpecovnik

config/sources/families/rockchip.conf

@@ -237,8 +237,8 @@ family_tweaks() {
 
 	# Create gpio and i2c groups on the build rootfs; they are matched against
 	# udev rules to allow non-root user access to these resources
-	chroot_sdcard addgroup --system --quiet --gid 900 gpio
-	chroot_sdcard addgroup --system --quiet --gid 901 i2c
+	chroot_sdcard getent group gpio >/dev/null || chroot_sdcard addgroup --system --quiet --gid 900 gpio
+	chroot_sdcard getent group i2c  >/dev/null || chroot_sdcard addgroup --system --quiet --gid 901 i2c
 
 	return 0