ASoC: msm: Decrease the playback period size of PCM driver

To support the deep buffer output, the playback buffer size is
increased to 4k from 2k. Reverting the change as the support for
deep buffer output is no longer valid.

Change-Id: I5034245bde4b55a5816506fbdfeac970a8e7804b
CRs-Fixed: 438177
Signed-off-by: Subhash Chandra Bose Naripeddy <snariped@codeaurora.org>