csky: fix arch_jump_label_transform_static override

The arch_jump_label_transform_static() function in csky was originally meant to
override the generic __weak function, but that got changed to an #ifndef check.

This showed up as a missing-prototype warning:
arch/csky/kernel/jump_label.c:43:6: error: no previous prototype for 'arch_jump_label_transform_static' [-Werror=missing-prototypes]

Change the method to use the new method of having a #define and a prototype
for the global function.

Fixes: 7e6b9db2 ("jump_label: make initial NOP patching the special case")
Fixes: 4e8bb4ba ("csky: Add jump-label implementation")
Reviewed-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/csky/include/asm/jump_label.h

@@ -43,5 +43,10 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key,
 	return true;
 }
 
+enum jump_label_type;
+void arch_jump_label_transform_static(struct jump_entry *entry,
+				      enum jump_label_type type);
+#define arch_jump_label_transform_static arch_jump_label_transform_static
+
 #endif  /* __ASSEMBLY__ */
 #endif	/* __ASM_CSKY_JUMP_LABEL_H */