um: segv: Save regs only in case of a kernel mode fault

...otherwise me lose user mode regs and the resulting
stack trace is useless.
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/kernel/trap.c

@@ -206,7 +206,7 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
 	int is_write = FAULT_WRITE(fi);
 	unsigned long address = FAULT_ADDRESS(fi);
 
-	if (regs)
+	if (!is_user && regs)
 		current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
 
 	if (!is_user && (address >= start_vm) && (address < end_vm)) {