KVM: shut up uninit compiler warning in paging_tmpl.h

Dixes compilation warning:
  CC      arch/x86/kernel/io_delay.o
 arch/x86/kvm/paging_tmpl.h: In function ‘paging64_fetch’:
 arch/x86/kvm/paging_tmpl.h:279: warning: ‘sptep’ may be used uninitialized in this function
 arch/x86/kvm/paging_tmpl.h: In function ‘paging32_fetch’:
 arch/x86/kvm/paging_tmpl.h:279: warning: ‘sptep’ may be used uninitialized in this function

warning is bogus (always have a least one level), but need to shut the compiler
up.

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Avi Kivity <avi@redhat.com>