Relax source check in a keyboard CTS test

This change allows this CTS to pass with both kernel prior to 4.18 and
kernels 4.18 or above. Linux introduces a behavior change in 4.18 that
splits this keyboard into 2 input devices, and further divide Android
input devices into 2. Therefore the source reported by
KeyboardInputMapper also changes.

Bug: 147917677
Test: atest MicrosoftDesignerKeyboardTest passes on both crosshatch and
cf_phone_x86.

Change-Id: I2242e8150ae44dfb0dc40f6bde0f42cc8170dc6a