s390/seccomp: fix error return for filtered system calls

The syscall_set_return_value function of s390 negates the error argument
before storing the value to the return register gpr2. This is incorrect,
the seccomp code already passes the negative error value.
Store the unmodified error value to gpr2.

Signed-off-by: Jan Willeke <willeke@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/syscall.h

@@ -54,7 +54,7 @@ static inline void syscall_set_return_value(struct task_struct *task,
 					    struct pt_regs *regs,
 					    int error, long val)
 {
-	regs->gprs[2] = error ? -error : val;
+	regs->gprs[2] = error ? error : val;
 }
 
 static inline void syscall_get_arguments(struct task_struct *task,