x86/traps: 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>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

xen/arch/x86/traps.c

@@ -123,7 +123,7 @@ unsigned int __ro_after_init ler_msr;
 const unsigned int nmi_cpu;
 
 #define stack_words_per_line 4
-#define ESP_BEFORE_EXCEPTION(regs) ((unsigned long *)regs->rsp)
+#define ESP_BEFORE_EXCEPTION(regs) ((unsigned long *)(regs)->rsp)
 
 void show_code(const struct cpu_user_regs *regs)
 {