Change assert statement to GST_ELEMENT_ERROR
Change assert statement to GST_ELEMENT_ERROR

Changed to use GST_ELEMENT_ERROR instead of using assert statement
when pipeline could not be configured.

Change-Id: I7034f4ef0a16a47ce01f224c646be0091bc053ae
Reviewed-on: https://gpro.palm.com/39923
Reviewed-by: HoonHee Lee <41497318ef67053f37c2ac0e974a3369f66d66ec@lge.com>
Reviewed-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>
Tested-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>
(cherry picked from commit b953a983a1e35629becb9cb367b7ccfa1466941f)

justinjoy/gst-plugins-cool,justinjoy/gst-plugins-cool