usb: serial: silence all non-critical read errors
usb: serial: silence all non-critical read errors

If a USB serial device is unplugged while there is an active program
using the device it may spam the logs with -EPROTO (71) messages as it
attempts to retry.

Most serial usb drivers (metro-usb, pl2303, mos7840, ...) only output
these messages for debugging.  The generic driver treats these as
errors.

Change the default output for the generic serial driver from error to
debug to silence these non-critical errors.

Signed-off-by: Jeremiah Mahler <0c597d45353d741b4835ff5e56c2bc263abede5d@gmail.com>
Signed-off-by: Johan Hovold <759412786bc533369b22377bf83fb9056c5b25b2@kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs