do_vfs_ioctl(): use saner types

casting to pointer to int, only to pass that to function that
takes pointer to void and uses it as pointer to structure is
really asking for trouble.

"Some pointer, I'm not sure what to" is spelled "void *",
not "int *"; use that.

And declare the functions we are passing that pointer to
as taking the pointer to what they really want to access.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>