drivers: use kzalloc/kcalloc instead of 'kmalloc+memset', where possible

Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
Cc: Jeff Garzik <jgarzik@pobox.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Tejun Heo <tj@kernel.org>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>