arch/tile: fix futex sanitization definition/prototype mismatch

Commit 8d7718aa

 changed "int"
to "u32" in the prototypes but not the definition.
I missed this when I saw the patch go by on LKML.

We cast "u32 *" to "int *" since we are tying into the underlying
atomics framework, and atomic_t uses int as its value type.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Reviewed-by: Michel Lespinasse <walken@google.com>