kvm tools: arm: fix fallout from debug_fd refactoring

Commit 21692d19f744 ("kvm tools: Beautify debug output") changed the
kvm__dump_mem prototype but only fixed up calls from x86.

This patch fixes arm to pass the debug_fd as required.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>