fs/compat: fix lookup_dcookie() parameter handling

fs/compat: fix lookup_dcookie() parameter handling

Commit d5dc77bfeeab ("consolidate compat lookup_dcookie()") coverted all
architectures to the new compat_sys_lookup_dcookie() syscall.

The "len" paramater of the new compat syscall must have the type
compat_size_t in order to enforce zero extension for architectures where
the ABI requires that the caller of a function performed zero and/or
sign extension to 64 bit of all parameters.

Signed-off-by: Heiko Carstens <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Hendrik Brueckner <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: <[email protected]>	[v3.10+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>