docs: Fix GstBuffer typo "memory bock" -> "memory block"
docs: Fix GstBuffer typo "memory bock" -> "memory block"

https://bugzilla.gnome.org/show_bug.cgi?id=737117

centricular/gstreamer,StreamUtils/gstreamer,mparis/gstreamer,mparis/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,centricular/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,centricular/gstreamer,mparis/gstreamer,mparis/gstreamer