[media] cx231xx: simplify I2C scan debug messages

Don't need to show when it starts or stops. Just print lines
when devices are found.

After the changes, the output for i2c scan will be like:

	usb 1-2: i2c scan: found device @ port 0 addr 0x40  [???]
	usb 1-2: i2c scan: found device @ port 0 addr 0x60  [colibri]
	usb 1-2: i2c scan: found device @ port 0 addr 0x88  [hammerhead]
	usb 1-2: i2c scan: found device @ port 0 addr 0x98  [???]
	usb 1-2: i2c scan: found device @ port 3 addr 0xa0  [eeprom]
	usb 1-2: i2c scan: found device @ port 2 addr 0x60  [colibri]
	usb 1-2: i2c scan: found device @ port 2 addr 0xc0  [tuner]
	usb 1-2: i2c scan: found device @ port 4 addr 0x20  [demod]

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>