ATM-nicstar: Refactor a kmalloc() call in ns_init_card()

* The script "checkpatch.pl" can point out that assignments should usually
  not be performed within condition checks.
  Thus move an assignment for a local variable to a separate statement
  in this function.

* Replace the specification of a data structure by a pointer dereference
  as the parameter for the operator "sizeof" to make the corresponding size
  determination a bit safer according to the Linux coding style convention.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: David S. Miller <davem@davemloft.net>