[IA64] sn: Do not needlessly convert between pointers and integers

The nasid_to_try variable is an array of integers, so plain integers can
be used when assigning values to the elements rather than casting a NULL
pointer to an integer, which results in the following warning from GCC:

	arch/ia64/sn/kernel/bte.c:117:22: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
	    nasid_to_try[1] = (int)NULL;
	                      ^
	arch/ia64/sn/kernel/bte.c:125:22: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
	    nasid_to_try[1] = (int)NULL;
	                      ^

Replace (int)NULL with a simple 0 to silence these warnings.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>