[media] drxd: use kzalloc in drxd_attach()

This saves a little .text and removes the sizeof(...) style
inconsistency. Use sizeof(*state) in accordance with CodingStyle.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>