[media] tuner-xc2028: 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/tuners/tuner-xc2028.c:651:1: warning: 'load_firmware' uses dynamic stack allocation [enabled by default]
Instead, let's enforce a limit for the buffer.
In the specific case of this driver, the maximum limit is 80, used only
on tm6000 driver. This limit is due to the size of the USB control URBs.
Ok, it would be theoretically possible to use a bigger size on PCI
devices, but the firmware load time is already good enough. Anyway,
if some usage requires more, it is just a matter of also increasing
the buffer size at load_firmware().

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>