[media] cx18: struct i2c_client is too big for stack

[media] cx18: struct i2c_client is too big for stack

	drivers/media/pci/cx18/cx18-driver.c: In function 'cx18_read_eeprom':
	drivers/media/pci/cx18/cx18-driver.c:357:1: warning: the frame size of 1072 bytes is larger than 1024 bytes [-Wframe-larger-than=]
That happens because the routine allocates 256 bytes for an eeprom buffer, plus
the size of struct i2c_client, with is big.
Change the logic to dynamically allocate/deallocate space for struct i2c_client,
instead of  using the stack.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Reviewed-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>