asoc: set min period size of capture/playback to 120

sound card open failed for capture with 128 16-bit samples at 24 kHz
because min period size of cupture is set to 320.

Change-Id: Ida818ef133e6ac6e282c798559a753618b1d1e28
Signed-off-by: Deru Wang <deruwang@codeaurora.org>