hikey960: fix build issue with CLANG

plat/hisilicon/hikey960/drivers/pwrc/hisi_pwrc.c:290:20:
error: unused function 'hisi_pdc_set_intmask' [-Werror,-Wunused-function]
static inline void hisi_pdc_set_intmask(void *pdc_base_addr,
                   ^
1 error generated.
Makefile:605: recipe for target 'build/hikey960/release/bl31/hisi_pwrc.o' failed
make: *** [build/hikey960/release/bl31/hisi_pwrc.o] Error 1
Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>

plat/hisilicon/hikey960/drivers/pwrc/hisi_pwrc.c

@@ -287,9 +287,9 @@ void hisi_enable_pdc(unsigned int cluster)
 	mmio_write_32((uintptr_t)pdc_base_addr, 0x1);
 }
 
-static inline void hisi_pdc_set_intmask(void *pdc_base_addr,
-					unsigned int core,
-					enum pdc_finish_int_mask intmask)
+void hisi_pdc_set_intmask(void *pdc_base_addr,
+			unsigned int core,
+			enum pdc_finish_int_mask intmask)
 {
 	unsigned int val;