greybus: greybus_protocols: fix guard tag

I neglected to update the "#ifndef/#define" when I renamed
"greybus_protocols.h".  Fix that.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>