x86_64/cpu_idle: address violations of MISRA C Rule 20.7

MISRA C Rule 20.7 states: "Expressions resulting from the expansion
of macro parameters shall be enclosed in parentheses". Therefore, some
macro definitions should gain additional parentheses to ensure that all
current and future users will be safe with respect to expansions that
can possibly alter the semantics of the passed-in macro parameter.

No functional change.

Signed-off-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/x86_64/cpu_idle.c

@@ -93,7 +93,7 @@ long compat_set_cx_pminfo(uint32_t acpi_id,
             return -EFAULT; \
         guest_from_compat_handle(states, (_s_)->states); \
 \
-        for ( i = 0; i < _s_->count; i++ ) \
+        for ( i = 0; i < (_s_)->count; i++ ) \
         { \
            if ( unlikely(copy_from_guest_offset(&state, states, i, 1)) ) \
                return -EFAULT; \