greybus: fix version check

greybus: fix version check

When we read a module manifest we are required to verify that its
version is compatible with the version the present code is able
to parse.  All that's required is a check of the major version
number.  If the manifest's major version is greater than the
software, the software can't assume it can parse it.  All new
code must be able to parse all old versions of the format.  And
any difference in minor version is supposed to have no effect
on parsability.

Update the version check to enforce this policy, and reword the
error message to do a better job of explaining the situation.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>