Incorrect use of 0 in terminating entry of arch_tables[] causes the
following sparse warning,
  arch/x86/platform/efi/efi.c:74:27: sparse: Using plain integer as NULL pointer
Replace with NULL.
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
[ Included sparse warning in commit message. ]
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
 #ifdef CONFIG_X86_UV
        {UV_SYSTEM_TABLE_GUID, "UVsystab", &efi.uv_systab},
 #endif
-       {NULL_GUID, NULL, 0},
+       {NULL_GUID, NULL, NULL},
 };
 
 /*