KVM: SVM: Clean up handling of LBR virtualization enabled

Clean up the enable_lbrv computation in svm_update_lbrv() to consolidate
the logic for computing enable_lbrv into a single statement, and to remove
the coding style violations (lack of curly braces on nested if).

No functional change intended.

Link: https://lore.kernel.org/r/20230607203519.1570167-3-seanjc@google.com


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