silo: include stddef.h in stringops.h

I recompiled toolchain/glibc/everything from scratch against Linux 3.4
headers and silo won't compile anymore:

	file.c:60:5: error: 'NULL' undeclared here (not in a function)
	fs/ext2.c:401:7: error: 'NULL' undeclared (first use in this function)
	fs/isofs.c:57:45: error: 'NULL' undeclared (first use in this function)
	etc.

Fix by including stddef.h.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed