bdinfo: x86: vesa: Update fb_base to the correct value

Set this value in global_data so that it is reported correctly on x86
boards.

In fact, U-Boot allocates space for the frame buffer even though it is not
used. Then the FSP picks the address itself (e.g. 0xb0000000). So the
value set by U-Boot (high in memory with everything else that is
relocated), is not actually the correct value.

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