MIPS: asm: syscall: Add the syscall_rollback function

The syscall_rollback function is used by seccomp-bpf but it was never
added for MIPS. It doesn't need to do anything as none of the registers
are clobbered if the system call has been denied by the seccomp filter.
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6403/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/syscall.h

@@ -65,6 +65,12 @@ static inline long syscall_get_return_value(struct task_struct *task,
 	return regs->regs[2];
 }
 
+static inline void syscall_rollback(struct task_struct *task,
+				    struct pt_regs *regs)
+{
+	/* Do nothing */
+}
+
 static inline void syscall_set_return_value(struct task_struct *task,
 					    struct pt_regs *regs,
 					    int error, long val)