Fix pointer type mismatch of handlers

Commit 4c0d03907652 ("Rework type usage in Trusted Firmware") changed
the type usage in struct declarations, but did not touch the definition
side.  Fix the type mismatch.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/plat/rockchip/rk3399/plat_sip_calls.c b/plat/rockchip/rk3399/plat_sip_calls.c
index 2fbda67..ae74c9c 100644
--- a/plat/rockchip/rk3399/plat_sip_calls.c
+++ b/plat/rockchip/rk3399/plat_sip_calls.c
@@ -47,14 +47,14 @@
 	return 0;
 }
 
-uint64_t rockchip_plat_sip_handler(uint32_t smc_fid,
-				   uint64_t x1,
-				   uint64_t x2,
-				   uint64_t x3,
-				   uint64_t x4,
-				   void *cookie,
-				   void *handle,
-				   uint64_t flags)
+uintptr_t rockchip_plat_sip_handler(uint32_t smc_fid,
+				    u_register_t x1,
+				    u_register_t x2,
+				    u_register_t x3,
+				    u_register_t x4,
+				    void *cookie,
+				    void *handle,
+				    u_register_t flags)
 {
 	uint64_t x5, x6;