x86/cpuid: address violation of MISRA C Rule 16.2

x86/cpuid: address violation of MISRA C Rule 16.2

Refactor the switch so that a violation of MISRA C Rule 16.2 is resolved
(A switch label shall only be used when the most closely-enclosing
compound statement is the body of a switch statement).
Note that the switch clause ending with the pseudo
keyword "fallthrough" is an allowed exception to Rule 16.3.

No functional change.

Signed-off-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Acked-by: Jan Beulich <jbeulich@suse.com>