mm: prevent a warning when casting void* -> enum

mm: prevent a warning when casting void* -> enum

I recently build the RISC-V port with LLVM trunk, which has introduced a
new warning when casting from a pointer to an enum of a smaller size.
This patch simply casts to a long in the middle to stop the warning.  I'd
be surprised this is the only one in the kernel, but it's the only one I
saw.

Signed-off-by: Palmer Dabbelt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>