HID: wacom: Remove comparison of u8 mode with zero and simplify.

Variable mode in method wacom_show_remote_mode() is defined as u8, thus
statement (mode >= 0) is always true and should be removed, simplifying
the logic.

Signed-off-by: Christos Gkekas <chris.gekas@gmail.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>