x86, kvm: Remove cast obsoleted by set_64bit() prototype cleanup

KVM ended up having to put a pretty ugly wrapper around set_64bit()
in order to get the type right.  Now set_64bit() takes the expected
u64 type, and this wrapper can be cleaned up.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Avi Kivity <avi@redhat.com>
LKML-Reference: <4C5C4E7A.8040603@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>