media: video/hdmi: handle short reads of hdmi info frame.

Calling hdmi_infoframe_unpack() with static sizeof(buffer) skips all
the size checking done later in hdmi_infoframe_unpack().  A better
value is the amount of data read into buffer.

Fixes: 480b8b3e

 ("video/hdmi: Pass buffer size to infoframe unpack functions")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>