HID: wacom: Have wacom_{get,set}_report retry on -EAGAIN, not -EPIPE

Retrying on -EPIPE makes very little sense since this typically indicates
a problem that will not just disappear on its own. For instance, the USB
documentation states that it will be sent if the endpoint is stalled or
the device has disconnected. Instead, we should retry if -EAGAIN is
received since this indicates a temporary error condition such as a busy
bus.

In addition to adjusting the conditions we retry under, we also log an
error on failure so that we can be aware of what's going on.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>