swr: Fix build with llvm-9.0 again.
Commit 6f7306c0 ("swr/rast: Refactor memory API between rasterizer core and swr") unintentionally removed changes for llvm-9.0.
Fixes: 6f7306c0 ("swr/rast: Refactor memory API between rasterizer core and swr") Fixes: 5dd9ad15 ("swr/rasterizer: Better implementation of scatter") Signed-off-by: Vinson Lee vlee@freedesktop.org