vbe: Drop the U-Boot prefix from the version

vbe: Drop the U-Boot prefix from the version

We don't need the U-Boot prefix on the version and in fact it is harmful
since pytest gets confused seeing the U-Boot banner bring displayed when
the version is printed.

Drop the prefix from the string.

We could produce an entirely new string from the component parts, but this
adds to the rodata size and would break the use of version_string as the
only thing which holds this information.

Signed-off-by: Simon Glass <sjg@chromium.org>