Give typo in kernel-doc documentation: hdr -> hrd

Fixes this warning:

drivers/media/platform/allegro-dvt/nal-h264.h:33: warning: expecting prototype for struct nal_h264_hdr_parameters. Prototype was for struct
nal_h264_hrd_parameters instead
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>