tbs5520se.c - remove green artifacts by increasing .buffersize

[nvdias0]

I've noticed green artifacts in some transmissions when using a a tbs5520se based receiver.
This happens for both SAT and CABLE.

changing .buffersize in tbs5520se.c from 4096 to 8192 solves the issue.
in struct definition
static struct dvb_usb_device_properties tbs5520se_properties

I suggest adding it to the source code.