fastboot: remove retries on invalid IO iterator in OSX

When IOServiceGetMatchingServices returns an invalid
iterator, IOIteratorReset doesn't help. Break the loop
to prevent being stuck in the reset loop forever.
This should be fine as the open_device() call in the
upper layer is already doing retries.

Bug: 286495045
Test: fastboot update
Change-Id: Ia58fa9285640be34aa22cd77e4f58cc9092679a4