Fix a coding style issue in trusty.c

This patch fixes the following coding style error reported
by the checkpatch.pl script:

  Bad function definition - void el3_exit() should probably
  be void el3_exit(void)

There is another one but it's a false positive so there's no
point in fixing it:

  space prohibited after that '&' (ctx:WxW)
  +#define SMC_NR(entity, fn, fastcall, smc64) ((((fastcall) & 0x1) << 31) | \
                                                            ^
Change-Id: I34de0337c7216dabd16395879f13845a60ee6df0
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>

services/spd/trusty/trusty.c

@@ -229,7 +229,7 @@ static uint64_t trusty_smc_handler(uint32_t smc_fid,
 
 static int32_t trusty_init(void)
 {
-	void el3_exit();
+	void el3_exit(void);
 	entry_point_info_t *ep_info;
 	struct trusty_cpu_ctx *ctx = get_trusty_ctx();
 	uint32_t cpu = plat_my_core_pos();