Stub out dcd_edpt_close for samd

[maddyaby]

Not having this prevents the device from finishing the mounting process.

Tested on a SAMD51 and didn't seem to need to actually do anything in the close function. Did repeated close/opens of an audio streaming endpoint.

[hathach]

dcd_edpt_close() is mostly used by audio with ISO endpoint, since SAMD doesn't support/test with ISO, it is left out. Have you manage to get audio example running with samd51 ?

[maddyaby]

I got a streaming application working with SAMD51 (audio streaming from computer to device using ISO OUT endpoint). I needed to stub this out though for the calls in audio_device.c / audiod_set_interface to finish correctly.

[hathach]

thank you for testing out, samd is not tested with ISO yet. Though indeed, this will allow it to enumerate and do a bit more testing.