KVM: PPC: E500: Compile fix in this_cpu_write

Commit 69111bac

 ("powerpc: Replace __get_cpu_var uses") introduced
compile breakage to the e500 target by introducing invalid automatically
created C syntax.

Fix up the breakage and make the code compile again.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>