PC, KVM, CMA: Fix regression caused by wrong get_order() use

PC, KVM, CMA: Fix regression caused by wrong get_order() use

fc95ca7284bc54953165cba76c3228bd2cdb9591 claims that there is no
functional change but this is not true as it calls get_order() (which
takes bytes) where it should have called order_base_2() and the kernel
stops on VM_BUG_ON().

This replaces get_order() with order_base_2() (round-up version of ilog2).

Suggested-by: Paul Mackerras <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Reviewed-by: Aneesh Kumar K.V <[email protected]>
Signed-off-by: Alexey Kardashevskiy <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>