ARM: KVM: Work around older compiler bug

Compilers before 4.6 do not behave well with unnamed fields in structure
initializers and therefore produces build errors:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676



By refering to the unnamed union using braces, both older and newer
compilers produce the same result.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Reported-by: Russell King <linux@arm.linux.org.uk>
Tested-by: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>