media: dvb-usb: Fix error handling in dvb_usb_i2c_init

In dvb_usb_i2c_init, if i2c_add_adapter fails, it only prints an error
message, and then continues to set DVB_USB_STATE_I2C. This affects the
logic of dvb_usb_i2c_exit, which leads to that, the deletion of i2c_adap
even if the i2c_add_adapter fails.

Fix this by returning at the failure of i2c_add_adapter and then move
dvb_usb_i2c_exit out of the error handling code of dvb_usb_i2c_init.

Fixes: 13a79f14 ("media: dvb-usb: Fix memory leak at error in dvb_usb_device_init()")
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>