staging/ft1000: fix sparse warning
staging/ft1000: fix sparse warning

sparse warns about having 0 assigned to a pointer,
fix it up by using NULL.

The following sparse warning is fixed

drivers/staging/ft1000/ft1000-usb/ft1000_debug.c:170:52: warning: Using plain integer as NULL pointer

Signed-off-by: Devendra Naga <97fdf9fb34d40445b99f4e064a18057cd6e2bccb@gmail.com>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs