hv:fix "missing for discarded return value" for memset

No need to check the return value for memset
code like this:
int a(void) {
	return 0;
}
int b(void){
	a();
}
fix as follow:
int a(void) {
	return 0;
}
int b(void){
	(void)a();
}

Signed-off-by: Mingqiang Chi <mingqiang.chi@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/debug/printf.c

@@ -45,7 +45,7 @@ int vprintf(const char *fmt, va_list args)
 	int nchars = 0;
 
 	/* initialize parameters */
-	memset(&param, 0, sizeof(param));
+	(void)memset(&param, 0, sizeof(param));
 	param.emit = charout;
 	param.data = &nchars;