media: dvb_ca_en50221: fix a size write bug

media: dvb_ca_en50221: fix a size write bug

The function of "dvb_ca_en50221_write_data" at source/drivers/media
/dvb-core/dvb_ca_en50221.c is used for two cases.
The first case is for writing APDU data in the function of
"dvb_ca_en50221_io_write" at source/drivers/media/dvb-core/
dvb_ca_en50221.c.
The second case is for writing the host link buf size on the
Command Register in the function of "dvb_ca_en50221_link_init"
at source/drivers/media/dvb-core/dvb_ca_en50221.c.
In the second case, there exists a bug like following.
In the function of the "dvb_ca_en50221_link_init",
after a TV host calculates the host link buf_size,
the TV host writes the calculated host link buf_size on the
Size Register.
Accroding to the en50221 Spec (the page 60 of
https://dvb.org/wp-content/uploads/2020/02/En50221.V1.pdf),
before this writing operation, the "SW(CMDREG_SW)" flag in the
Command Register should be set. We can see this setting operation
in the function of the "dvb_ca_en50221_link_init" like below.
...
	if ((ret = ca->pub->write_cam_control(ca->pub, slot,
CTRLIF_COMMAND, IRQEN | CMDREG_SW)) != 0)
		return ret;
...
But, after that, the real writing operation is implemented using
the function of the "dvb_ca_en50221_write_data" in the function of
"dvb_ca_en50221_link_init", and the "dvb_ca_en50221_write_data"
includes the function of "ca->pub->write_cam_control",
and the function of the "ca->pub->write_cam_control" in the
function of the "dvb_ca_en50221_wrte_data" does not include
"CMDREG_SW" flag like below.
...
	if ((status = ca->pub->write_cam_control(ca->pub, slot,
CTRLIF_COMMAND, IRQEN | CMDREG_HC)) != 0)
...
In the above source code, we can see only the "IRQEN | CMDREG_HC",
but we cannot see the "CMDREG_SW".
The "CMDREG_SW" flag which was set in the function of the
"dvb_ca_en50221_link_init" was rollbacked by the follwoing function
of the "dvb_ca_en50221_write_data".
This is a bug. and this bug causes that the calculated host link buf_size
is not properly written in the CI module.
Through this patch, we fix this bug.

Link: https://lore.kernel.org/linux-media/20220818125027.1131-1-yongsuyoo0215@gmail.com
Signed-off-by: YongSu Yoo <yongsuyoo0215@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>