Staging: wlags49_h2: Fix sparse warnings in sta_h2.c

This patch fixes sparse warnings "Using plain integer as NULL pointer" in
sta_h2.c

Signed-off-by: Monam Agarwal <monamagarwal123@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>