Now that the WRMSR fastpath for x2APIC_ICR and TSC_DEADLINE are identical,
ignoring the backend MSR handling, consolidate the common bits of skipping
the instruction and setting the return value.

No functional change intended.

Link: https://lore.kernel.org/r/20240802195120.325560-3-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>