Fix uninitialized 'copy' in unshare_files

	Arrgghhh...

Sorry about that, I'd been sure I'd folded that one, but it actually got
lost.  Please apply - that breaks execve().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>