pluginloader: fix compiler warnings
pluginloader: fix compiler warnings

Cast string constants to make compiler happy.

krieger-od/gstreamer,krieger-od/gstreamer,mparis/gstreamer,drothlis/gstreamer,cablelabs/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,krieger-od/gstreamer,cablelabs/gstreamer,krichter722/gstreamer,magcius/gstreamer,ensonic/gstreamer,centricular/gstreamer,justinjoy/gstreamer,surround-io/gstreamer,ensonic/gstreamer,mparis/gstreamer,cfoch/gstreamer,centricular/gstreamer,jpakkane/gstreamer,justinjoy/gstreamer,ylatuya/gstreamer,ensonic/gstreamer,ahmedammar/platform_external_gst_gstreamer,surround-io/gstreamer,ensonic/gstreamer,lovebug356/gstreamer,cfoch/gstreamer,lovebug356/gstreamer,cablelabs/gstreamer,lovebug356/gstreamer,Distrotech/gstreamer,collects/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,centricular/gstreamer,jpxiong/gstreamer,lubosz/gstreamer,ylatuya/gstreamer,Lachann/gstreamer,magcius/gstreamer,shelsonjava/gstreamer,ahmedammar/platform_external_gst_gstreamer,Distrotech/gstreamer,ahmedammar/platform_external_gst_gstreamer,magcius/gstreamer,jpakkane/gstreamer,jpakkane/gstreamer,StreamUtils/gstreamer,Distrotech/gstreamer,krieger-od/gstreamer,mparis/gstreamer,centricular/gstreamer,collects/gstreamer,ensonic/gstreamer,shelsonjava/gstreamer,Lachann/gstreamer,collects/gstreamer,jpxiong/gstreamer,drothlis/gstreamer,mparis/gstreamer,collects/gstreamer,Distrotech/gstreamer,jpakkane/gstreamer,lubosz/gstreamer,shelsonjava/gstreamer,magcius/gstreamer,StreamUtils/gstreamer,lovebug356/gstreamer,mparis/gstreamer,justinjoy/gstreamer,jpxiong/gstreamer,cfoch/gstreamer,surround-io/gstreamer,magcius/gstreamer,cfoch/gstreamer,Lachann/gstreamer,krichter722/gstreamer,justinjoy/gstreamer,StreamUtils/gstreamer,Distrotech/gstreamer,drothlis/gstreamer,ylatuya/gstreamer,ylatuya/gstreamer,drothlis/gstreamer,krichter722/gstreamer,surround-io/gstreamer,Lachann/gstreamer,lubosz/gstreamer,krichter722/gstreamer,lubosz/gstreamer,cablelabs/gstreamer,jpxiong/gstreamer,collects/gstreamer,centricular/gstreamer,lovebug356/gstreamer,cfoch/gstreamer,jpakkane/gstreamer,ylatuya/gstreamer,krieger-od/gstreamer,ahmedammar/platform_external_gst_gstreamer,cablelabs/gstreamer,drothlis/gstreamer,ahmedammar/platform_external_gst_gstreamer,surround-io/gstreamer,justinjoy/gstreamer,lubosz/gstreamer,Lachann/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer