gltransformation: let graphene alloc its structures memory aligned

gltransformation: let graphene alloc its structures memory aligned

With NEON instructions enabled, graphene expects the memory passed to it
16-byte-aligned. Otherwise unaligned memory access faults occur causing
SIGBUS signals.

graphene has alloc functions for its structures that take care of this,
so use them.

See also: https://github.com/ebassi/graphene/issues/215#issuecomment-794744829

Suggested-by: Sebastian Dröge <sebastian@centricular.com>
Signed-off-by: Bastian Krause <bst@pengutronix.de>
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1321>