HID: logitech-hidpp: avoid repeated "multiplier = " log messages

These messages appear each time the mouse wakes from sleep, in my case
(Logitech M705), every minute or so.
Let's downgrade them to the "debug" level so they don't fill the kernel log
by default.

While we are at it, let's make clear that this is a wheel multiplier (and
not, for example, XY movement multiplier).

Fixes: 4435ff2f

 ("HID: logitech: Enable high-resolution scrolling on Logitech mice")
Cc: stable@vger.kernel.org
Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Reviewed-by: Harry Cutts <hcutts@chromium.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>