cw1200: Introduce the use of devm_kzalloc

This patch introduces the use of devm_kzalloc and does away with the
kfrees in the probe and remove functions.

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>