media: rcar_jpu: fix two kernel-doc markups

On kernel-doc, struct declarations should be declared as "struct foo".

Fix the following warnings:
	drivers/media/platform/rcar_jpu.c:265: warning: cannot understand function prototype: 'struct jpu_q_data '
	drivers/media/platform/rcar_jpu.c:281: warning: cannot understand function prototype: 'struct jpu_ctx '

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>