[media] cx231xx-i2c: reduce stack size in bus scan

The cx231xx_do_i2c_scan function needs a lot of stack because
it puts an i2c_client structure on it:

drivers/media/usb/cx231xx/cx231xx-i2c.c: In function 'cx231xx_do_i2c_scan':
drivers/media/usb/cx231xx/cx231xx-i2c.c:518:1: error: the frame size of 1248 bytes is larger than 1152 bytes [-Werror=frame-larger-than=]

This changes it to call i2c_transfer() directly instead, avoiding the
need for the structure.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>