AudioFlinger: allow small requested capacity for FAST path

AudioFlinger used to reject requests for the low latency FAST
path when the capacity was != mPipeFramesP2.
But if the caller requests < mPipeFramesP2 than we can just bump it
up to mPipeFramesP2 because the API allows that.

For example, on Pixel, mPipeFramesP2 is 4096

Bug: 80308183
Test: adb shell input_monitor_callback -pl -b4000 -m1
Test: should see performance mode 12 for LOW_LATENCY
Change-Id: I987067910de3194fb52370d0ea1626cffad6248c