ovs-ofctl: Workaround a compiler warning on MSVC.

MSVC complains about a void function returning a value if there is a
statement of the form - 'return foo()' even if foo() has a void return
type.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Acked-by: Ben Pfaff <blp@nicira.com>
hash.h: Avoid compiler warnings with MSVC.

The lack of 'const' in function declaration causes MSVC to complain
because the function definition uses it.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Acked-by: Ben Pfaff <blp@nicira.com>