arm64: fix syscall_fn_t type

Syscall wrappers in <asm/syscall_wrapper.h> use const struct pt_regs *
as the argument type. Use const in syscall_fn_t as well to fix indirect
call type mismatches with Control-Flow Integrity checking.
Signed-off-by: NSami Tolvanen <samitolvanen@google.com>
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/include/asm/syscall.h

@@ -20,7 +20,7 @@
 #include <linux/compat.h>
 #include <linux/err.h>
 
-typedef long (*syscall_fn_t)(struct pt_regs *regs);
+typedef long (*syscall_fn_t)(const struct pt_regs *regs);
 
 extern const syscall_fn_t sys_call_table[];