lpbin: fix to release sink when state has changed to NULL
lpbin: fix to release sink when state has changed to NULL

Change-Id: Ib53861f189423984fcb871aa8b9fee1e69e0e892
Reviewed-on: https://gpro.palm.com/6148
Tested-by: HoonHee Lee <41497318ef67053f37c2ac0e974a3369f66d66ec@lge.com>
Reviewed-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>

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