[media] nxt200x: increase write buffer size

The buffer size on nxt200x is not enough:

	...
	> Dec 20 10:52:04 rich kernel: [   31.747949] nxt200x: nxt200x_writebytes: i2c wr reg=002c: len=255 is too big!
	...

Increase it to 256 bytes.

Reported-by: Rich Freeman <rich0@gentoo.org>
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>