csky: Fixup compile error

Add header file for asmlinkage macro.

Error log:
In file included from arch/csky/include/asm/ptrace.h:7,
                 from arch/csky/include/asm/elf.h:6,
                 from include/linux/elf.h:6,
                 from kernel/extable.c:6:
arch/csky/include/asm/traps.h:43:11: error: expected ';' before 'void'
   43 | asmlinkage void do_trap_unknown(struct pt_regs *regs);
      |           ^~~~~

Fixes: c8171a86 ("csky: Fixup -Wmissing-prototypes warning")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>

arch/csky/include/asm/traps.h

@@ -3,6 +3,8 @@
 #ifndef __ASM_CSKY_TRAPS_H
 #define __ASM_CSKY_TRAPS_H
 
+#include <linux/linkage.h>
+
 #define VEC_RESET	0
 #define VEC_ALIGN	1
 #define VEC_ACCESS	2