lptsinkbin: disable async enable appsink
lptsinkbin: disable async enable appsink

In sparse stream cases, sink element can not get buffer when doing seek.
Then this element can not go to PAUSED state and pipeline will hanging.
Thus appsink element async is disabled.

:Issues Addressed:
[GF-56077] pipeline is hanging when doing seek

Change-Id: Ie1502fd9d756f3637a09bec087ab68b397fad0b8
Reviewed-on: https://gpro.palm.com/23139
Reviewed-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>
Tested-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>

justinjoy/gst-plugins-lp,justinjoy/gst-plugins-lp