ASoC: WCD9304: Wait for earpiece PA to settle down

During playback of audio on earpiece path, the PA on the path
is the last component to be turned on. The turn on of PA can
cause a glitch in the output signal because the level of the PA
is not yet settled. Waiting for 20 msec after turning on the PA
avoids this glitch.

CRs-fixed: 417031
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>
(cherry picked from commit 1fa994d4aa256a536523f116232c4822b3495400)

Change-Id: Iaa7a47526c71d8b037df3d09cf30ede296c21356
Signed-off-by: Neha Pandey <nehap@codeaurora.org>