libinput/connection: Ensure touchpad defaults are used

The previous logic would set `defaults` to the last found group.

Since a touchpad is a pointer, it would set `defaults` to point
to `[Libinput][Defaults][Pointer]`, and thus the next clause would
try to find `[Libinput][Defaults][Pointer][Touchpad]`, instead of the
expected `[Libinput][Defaults][Touchpad]`. That is, only if a default
was set for Pointer.

Signed-off-by: Samuel Dionne-Riel <samuel@dionne-riel.com>