usb: misc: Avoid excessive logging during disconnect

When the device is in the midst of being disconnected, calls to
usb_autopm_get_interface() may fail, and a ERR-level message is
printed. Callers of such I/O functions may repeatedly try calling
again, and could end up flooding the console leading to a watchdog
timeout. Replace these printks with DBG-level messages since the
device disconnection is normal and the errors they indicate are
usually benign.

CRs-fixed: 394256
Change-Id: Icf9000faa9001832734ff9c64cd903b375cc2017
Signed-off-by: Jack Pham <jackp@codeaurora.org>