ALSA: Fix regression in qalsaaudioinput.cpp

In QAlsaAudioInput::open(), one should check against the available
audio inputs and not the audio outputs.

Regression introduced in 5473621b

.

Task-number: QTBUG-62435
Change-Id: I5db0a092a98c17964c55c9358ea1010ca05e9d6f
Reviewed-by: Christian Stromme <christian.stromme@qt.io>