x86: fsp: Do not assert VPD_IMAGE_REV when DEBUG

When using different release version of Intel FSP, the VPD_IMAGE_REV
is different (ie: BayTrail Gold 3 is 0x0303 while Gold 4 is 0x0304).
Remove the asserting of this so that U-Boot does not hang in a debug
build.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>