arm64/efi: fix variable 'si' set but not used

GCC throws out this warning on arm64.

drivers/firmware/efi/libstub/arm-stub.c: In function 'efi_entry':
drivers/firmware/efi/libstub/arm-stub.c:132:22: warning: variable 'si'
set but not used [-Wunused-but-set-variable]

Fix it by making free_screen_info() a static inline function.
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/efi.h

@@ -105,7 +105,11 @@ static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
 	((protocol##_t *)instance)->f(instance, ##__VA_ARGS__)
 
 #define alloc_screen_info(x...)		&screen_info
-#define free_screen_info(x...)
+
+static inline void free_screen_info(efi_system_table_t *sys_table_arg,
+				    struct screen_info *si)
+{
+}
 
 /* redeclare as 'hidden' so the compiler will generate relative references */
 extern struct screen_info screen_info __attribute__((__visibility__("hidden")));