audio: restrict the force route condition

select_devices should only force route the
capture usecase(s) with snd_device that
shares the same backend with current
usecase.

For example, the "voice-call afe-proxy" doesn't
need to force route the device of audio-record
to be "voice-rx".

Bug: 113700667
Test: manual
Change-Id: I144c9b8e201b2331064cac62367b2839ceec9c9a
Signed-off-by: Carter Hsu <carterhsu@google.com>