hv:fixed several return value violations

-- change two timer callbacks to void type
-- ignore the return value for add_timer
-- add (void) before several functions(memset/memcpy/
   vcpu_get_xxx)

v1-->v2:
   ignore the return value for add_timer
Signed-off-by: Mingqiang Chi <mingqiang.chi@intel.com>
Reviewed-by: Junjie Mao <junjie.mao@intel.com>

hypervisor/include/arch/x86/timer.h

@@ -7,7 +7,7 @@
 #ifndef TIMER_H
 #define TIMER_H
 
-typedef int (*timer_handle_t)(void *data);
+typedef void (*timer_handle_t)(void *data);
 
 enum tick_mode {
 	TICK_MODE_ONESHOT = 0,