audit: correct a type mismatch in audit_syscall_exit()

audit_syscall_exit() saves a result of regs_return_value() in intermediate
"int" variable and passes it to __audit_syscall_exit(), which expects its
second argument as a "long" value.  This will result in truncating the
value returned by a system call and making a wrong audit record.

I don't know why gcc compiler doesn't complain about this, but anyway it
causes a problem at runtime on arm64 (and probably most 64-bit archs).

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Eric Paris <eparis@redhat.com>

include/linux/audit.h

@@ -137,7 +137,7 @@ static inline void audit_syscall_exit(void *pt_regs)
 {
 	if (unlikely(current->audit_context)) {
 		int success = is_syscall_success(pt_regs);
-		int return_code = regs_return_value(pt_regs);
+		long return_code = regs_return_value(pt_regs);
 
 		__audit_syscall_exit(success, return_code);
 	}