wlan: Use kzalloc instead of kmalloc

Currently driver is using kmalloc to allocate the
memory inside vod_mem_malloc api. Since kmalloc
don't set allocated memory to zero, memory allocated
is uninitialized which may contain some undefined
value and may result in undefined behaviour.

To resolve this issue use kzalloc instead of kmalloc
to allocate the memory which sets the allocated memory to
zero.

Change-Id: Idc1a697d9bbac5e9c08f153e46f125159daa3023
Crs-fixed: 2384090