KVM: x86: Drop double-underscores from __kvm_set_memory_region()

Now that there's no outer wrapper for __kvm_set_memory_region() and it's
static, drop its double-underscore prefix.

No functional change intended.

Cc: Tao Su <tao1.su@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Link: https://lore.kernel.org/r/20250111002022.1230573-5-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>