KVM: nSVM: Drop nested_vmcb_check_{save/control}() wrappers

KVM: nSVM: Drop nested_vmcb_check_{save/control}() wrappers

The wrappers provide little value and make it harder to see what KVM is
checking in the normal flow. Drop them.

Opportunistically fixup comments referring to the functions, adding '()'
to make it clear it's a reference to a function.

No functional change intended.

Co-developed-by: Sean Christopherson <seanjc@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260303003421.2185681-14-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>