sdcard_image-rpi.bbclass: shorten the default BOOTDD_VOLUME_ID
sdcard_image-rpi.bbclass: shorten the default BOOTDD_VOLUME_ID

* raspberrypi4-64 is 15 characters and with dosfstools-4.2 it breaks rootfs.rpi-sdimg with:
  mkfs.vfat: Label can be no longer than 11 characters
  mkfs.fat 4.2 (2021-01-31)

* introduced in:
  https://github.com/dosfstools/dosfstools/commit/c598354

Signed-off-by: Martin Jansa <516df3ff67e1fa5d153800b15fb204c0a1a389dc@gmail.com>

agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi