kvm: avoid collision with dprintf macro in stdio.h, spotted by clang

kvm: avoid collision with dprintf macro in stdio.h, spotted by clang

Fixes clang errors:
  CC    i386-softmmu/kvm.o
/src/qemu/target-i386/kvm.c:40:9: error: 'dprintf' macro redefined
In file included from /src/qemu/target-i386/kvm.c:21:
In file included from /src/qemu/qemu-common.h:27:
In file included from /usr/include/stdio.h:910:
/usr/include/bits/stdio2.h:189:12: note: previous definition is here
  CC    i386-softmmu/kvm-all.o
/src/qemu/kvm-all.c:39:9: error: 'dprintf' macro redefined
In file included from /src/qemu/kvm-all.c:23:
In file included from /src/qemu/qemu-common.h:27:
In file included from /usr/include/stdio.h:910:
/usr/include/bits/stdio2.h:189:12: note: previous definition is here

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>