staging: wilc1000: refactor wilc_set_multicast_list() function

Refactor wilc_set_multicast_list() by making below changes:
o use kmalloc_array
o remove unnecessary res
o add u8 *cur_mc
o use i as index
o use '%pM' extension in netdev_dbg()

The below checkpatch issue is also resolved after code refactor.
'spaces preferred around that '/' (ctx:VxV)'

Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>