lpsink: modify unsupported pipeline handling code
lpsink: modify unsupported pipeline handling code

:issues addressed:
[WEBOSLCD13-64467] infinite loading

Change-Id: Ib92a91867fa8e72e2a9b4c81c1043fb5734a972f
Reviewed-on: https://gpro.palm.com/32737
Tested-by: Wonchul Lee <9841bdbec9dbb2acc2dcaaa1dab0491399f0e464@lge.com>
Reviewed-by: WonHo Chun <0776ca6adb6a1e1d566ae6677b1353099e2d7f0f@lge.com>

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