Need reviewer - small type error found by VS2008 on 64bit Windows

[Kelly O'Hair]

Need reviewer - small type error found by VS2008 on 64bit Windows

6839126: Type error found by newer windows compiler
http://cr.openjdk.java.net/~ohair/jdk7/6839126-hotspot-psdk-type/webrev/

Definitely minor and not for m3.
Just need to get the jdk7/build forest in a state that it can be built
by the 64bit Windows SDK v6.1 (VS2008 compilers) again.
May push this changeset to jdk7/build/hotspot so we can proceed with this
Windows compiler upgrade work, will also push the changeset to the
jdk7/hotspot/hotspot repository once we get past this m3 madness... 8^}

-kto