buffer pool: put GstBufferPoolAcquireParams typedef before struct
buffer pool: put GstBufferPoolAcquireParams typedef before struct

Works around https://bugzilla.gnome.org/show_bug.cgi?id=581525

cablelabs/gstreamer,ensonic/gstreamer,cfoch/gstreamer,justinjoy/gstreamer,krichter722/gstreamer,collects/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,mparis/gstreamer,cablelabs/gstreamer,shelsonjava/gstreamer,lubosz/gstreamer,cablelabs/gstreamer,lubosz/gstreamer,justinjoy/gstreamer,centricular/gstreamer,ensonic/gstreamer,lovebug356/gstreamer,collects/gstreamer,justinjoy/gstreamer,lovebug356/gstreamer,jpakkane/gstreamer,shelsonjava/gstreamer,surround-io/gstreamer,centricular/gstreamer,Lachann/gstreamer,surround-io/gstreamer,surround-io/gstreamer,ensonic/gstreamer,krieger-od/gstreamer,mparis/gstreamer,centricular/gstreamer,jpxiong/gstreamer,lubosz/gstreamer,jpxiong/gstreamer,mparis/gstreamer,Lachann/gstreamer,jpakkane/gstreamer,lovebug356/gstreamer,justinjoy/gstreamer,jpakkane/gstreamer,shelsonjava/gstreamer,jpakkane/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,StreamUtils/gstreamer,Lachann/gstreamer,justinjoy/gstreamer,collects/gstreamer,krieger-od/gstreamer,jpxiong/gstreamer,lovebug356/gstreamer,ensonic/gstreamer,krieger-od/gstreamer,krichter722/gstreamer,jpakkane/gstreamer,cablelabs/gstreamer,cfoch/gstreamer,surround-io/gstreamer,Lachann/gstreamer,surround-io/gstreamer,krichter722/gstreamer,cfoch/gstreamer,collects/gstreamer,shelsonjava/gstreamer,StreamUtils/gstreamer,ensonic/gstreamer,centricular/gstreamer,cablelabs/gstreamer,mparis/gstreamer,lubosz/gstreamer,krieger-od/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,cfoch/gstreamer,krieger-od/gstreamer,StreamUtils/gstreamer,lubosz/gstreamer,lovebug356/gstreamer,Lachann/gstreamer,cfoch/gstreamer,collects/gstreamer,centricular/gstreamer,mparis/gstreamer