drm/atomic: Couple of typo fixes

s/seralization/serialization/
s/parallism/parallelism/

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>