[media] dw2102: Don't use dynamic static allocation

Dynamic static allocation is evil, as Kernel stack is too low, and
compilation complains about it on some archs:
	drivers/media/usb/dvb-usb/dw2102.c:368:1: warning: 'dw2102_earda_i2c_transfer' uses dynamic stack allocation [enabled by default]
	drivers/media/usb/dvb-usb/dw2102.c:449:1: warning: 'dw2104_i2c_transfer' uses dynamic stack allocation [enabled by default]
	drivers/media/usb/dvb-usb/dw2102.c:512:1: warning: 'dw3101_i2c_transfer' uses dynamic stack allocation [enabled by default]
	drivers/media/usb/dvb-usb/dw2102.c:621:1: warning: 's6x0_i2c_transfer' uses dynamic stack allocation [enabled by default]
Instead, let's enforce a limit for the buffer to be the max size of
a control URB payload data (64 bytes).

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>