ALSA: usb-audio: Add retry on -EPROTO from usb_set_interface()

During initialisation of Focusrite USB audio interfaces, -EPROTO is
sometimes returned from usb_set_interface(), which sometimes prevents
the device from working: subsequent usb_set_interface() and
uac_clock_source_is_valid() calls fail.

This patch adds up to 5 retries in endpoint_set_interface(), with a
delay starting at 5ms and doubling each time. 5 retries was chosen to
allow for longer than expected waits for the interface to start
responding correctly; in testing, a single 5ms delay was sufficient to
fix the issue.

Closes: https://github.com/geoffreybennett/fcp-support/issues/2


Cc: stable@vger.kernel.org
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://patch.msgid.link/Z//7s9dKsmVxHzY2@m.b4.vu


Signed-off-by: Takashi Iwai <tiwai@suse.de>