Release string after gst_cap_to_string is called.
Release string after gst_cap_to_string is called.

Change-Id: I4bf8086e4413b4acb851d67919ac1014705bab03
Reviewed-by: Dmytro Poplavskiy <72e04cfb587e72184d425a79cb5cea0021f0b982@nokia.com>

jfaust/qtmultimedia,jfaust/qtmultimedia,mer-qt/qtmultimedia,nezticle/qtmultimedia,sergiusens/qtmultimedia,webOS-ports/qtmultimedia,webOS-ports/qtmultimedia,webOS-ports/qtmultimedia,jfaust/qtmultimedia,nezticle/qtmultimedia,webOS-ports/qtmultimedia,jfaust/qtmultimedia,mer-qt/qtmultimedia,sergiusens/qtmultimedia,mer-qt/qtmultimedia,sergiusens/qtmultimedia,sergiusens/qtmultimedia,sergiusens/qtmultimedia,jfaust/qtmultimedia,nezticle/qtmultimedia,nezticle/qtmultimedia,mer-qt/qtmultimedia,webOS-ports/qtmultimedia,nezticle/qtmultimedia,mer-qt/qtmultimedia