HID: usbhid: hid-pidff: Demote a couple kernel-doc abuses

Fixes the following W=1 kernel build warning(s):

 drivers/hid/usbhid/hid-pidff.c:512: warning: Function parameter or member 'dev' not described in 'pidff_playback'
 drivers/hid/usbhid/hid-pidff.c:512: warning: Function parameter or member 'effect_id' not described in 'pidff_playback'
 drivers/hid/usbhid/hid-pidff.c:512: warning: Function parameter or member 'value' not described in 'pidff_playback'
 drivers/hid/usbhid/hid-pidff.c:512: warning: expecting prototype for value times(). Prototype was for pidff_playback() instead
 drivers/hid/usbhid/hid-pidff.c:1005: warning: Function parameter or member 'pidff' not described in 'pidff_find_effects'
 drivers/hid/usbhid/hid-pidff.c:1005: warning: Function parameter or member 'dev' not described in 'pidff_find_effects'
 drivers/hid/usbhid/hid-pidff.c:1005: warning: expecting prototype for Find the implemented effect types(). Prototype was for pidff_find_effects() instead

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: Anssi Hannula <anssi.hannula@gmail.com>
Cc: linux-usb@vger.kernel.org
Cc: linux-input@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>