USB: cxacru: Use appropriate logging for errors

When an error occurs, existing logging uses dbg() so the cause of a
problem is hard to determine. Error conditions shouldn't only be
properly reported with debugging enabled.

A side effect of this change is that when an uninitialised device is
started, a log message similar to the following is sent:
	cxacru 5-2:1.0: receive of cm 0x90 failed (-104)
This is normal - the device did not respond so firmware will be loaded.

Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
Acked-by: Duncan Sands <baldrick@free.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>