x86: Alter nmi_callback_t typedef

Drop paranthesis and function pointer on nmi_callback_t typedef.

Make it more inline with how x86 maintainers want function
typedefs to be.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/alternative.c

@@ -192,7 +192,7 @@ static void __init apply_alternatives(struct alt_instr *start, struct alt_instr
 
 void __init alternative_instructions(void)
 {
-    nmi_callback_t saved_nmi_callback;
+    nmi_callback_t *saved_nmi_callback;
 
     arch_init_ideal_nops();
 

xen/arch/x86/traps.c

@@ -3611,7 +3611,7 @@ static int dummy_nmi_callback(const struct cpu_user_regs *regs, int cpu)
     return 0;
 }
  
-static nmi_callback_t nmi_callback = dummy_nmi_callback;
+static nmi_callback_t *nmi_callback = dummy_nmi_callback;
 
 void do_nmi(const struct cpu_user_regs *regs)
 {
@@ -3641,9 +3641,9 @@ void do_nmi(const struct cpu_user_regs *regs)
     }
 }
 
-nmi_callback_t set_nmi_callback(nmi_callback_t callback)
+nmi_callback_t *set_nmi_callback(nmi_callback_t *callback)
 {
-    nmi_callback_t old_nmi_callback = nmi_callback;
+    nmi_callback_t *old_nmi_callback = nmi_callback;
 
     nmi_callback = callback;
 

xen/include/asm-x86/nmi.h

@@ -12,7 +12,7 @@ extern bool_t opt_watchdog;
 /* Watchdog force parameter from the command line */
 extern bool_t watchdog_force;
  
-typedef int (*nmi_callback_t)(const struct cpu_user_regs *regs, int cpu);
+typedef int nmi_callback_t(const struct cpu_user_regs *regs, int cpu);
  
 /** 
  * set_nmi_callback
@@ -20,7 +20,7 @@ typedef int (*nmi_callback_t)(const struct cpu_user_regs *regs, int cpu);
  * Set a handler for an NMI. Only one handler may be
  * set. Return the old nmi callback handler.
  */
-nmi_callback_t set_nmi_callback(nmi_callback_t callback);
+nmi_callback_t *set_nmi_callback(nmi_callback_t *callback);
  
 /** 
  * unset_nmi_callback