kvm: avoid uninitialized-variable warnings

When PAGE_OFFSET is not a compile-time constant, we run into
warnings from the use of kvm_is_error_hva() that the compiler
cannot optimize out:

arch/arm/kvm/../../../virt/kvm/kvm_main.c: In function '__kvm_gfn_to_hva_cache_init':
arch/arm/kvm/../../../virt/kvm/kvm_main.c:1978:14: error: 'nr_pages_avail' may be used uninitialized in this function [-Werror=maybe-uninitialized]
arch/arm/kvm/../../../virt/kvm/kvm_main.c: In function 'gfn_to_page_many_atomic':
arch/arm/kvm/../../../virt/kvm/kvm_main.c:1660:5: error: 'entry' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This adds fake initializations to the two instances I ran into.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>