greybus: Fix probing of gpbridge devices

The gpbridge core tries to match the driver's id-table against all
CPorts available within the bundle for which the gpbridge bus was
created. The gpbdev here is unique for a cport_desc and only a single
cport_desc->protocol_id should be matched with the driver's id-table.

Fix it.

Tested on EVT 1.5 with a special manifest for GP module, where multiple
CPorts are part of the same Bridged PHY bundle.

Fixes: 75223f666687 ("gpbridge: implement gpbridge "bus" logic")
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>