platform/x86: asus-wmi: Simplify tablet-mode-switch probing

The 3 different tablet-mode-switch initialization paths repeat a lot
of the same code. Add a helper function for this.

This also makes the error-handling for the kbd_dock_devid case consistent
with the other 2 cases.

Cc: Luke D. Jones <luke@ljones.dev>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20220824151145.1448010-1-hdegoede@redhat.com