iwlagn: Convert kzalloc to kcalloc

Convert kzalloc to kcalloc, coalesce multiple lines too.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>