Add compat_ioctl support for VFAT_IOCTL_GET_VOLUME_ID

Add VFAT_IOCTL_GET_VOLUME_ID to vfat dir compat_ioctl() interface,
which enable you read vfat volume ID from a 32bit app on a 64bit
kernel

Change-Id: I3e93dfcc1e7a364a6b11bc7e3f5f210e82f306ed
Signed-off-by: Bintian Wang <bintian.wang@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>