V4L/DVB (11832): dibusb_mc: fix i2c to not corrupt eeprom in case of strange read pattern

dibusb_i2c_xfer seems to do things very dangerous :
it assumes that it get only write/read request or write request.

That means that read can be understood as write. For example a program
doing
file = open("/dev/i2c-x", O_RDWR);
    ioctl(file, I2C_SLAVE, 0x50)
read(file, data, 10)
    will corrupt the eeprom as it will be understood as a write.

Signed-off-by: Matthieu CASTET <castet.matthieu@free.fr>
Signed-off-by: Patrick Boettcher <pb@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>