greybus: endo: Rename endo's 'type' as 'id'

There can be three Endo types: mini, medium and large. And that's what
Endo 'type' should refer to.

But we have named the 16 bit number that uniquely represents a valid
endo, as its type. 'id' seems to be a more suitable name to that instead
of 'type'. Lets rename it.

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