arm: Return code correction for unw_step()

Let's not drop error code or zero-return unconditionally.

This has been incurring occasional indefinite loop in
dotnet core when it already had hit the bottom by
continously returning 1 from unw_step();

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>

src/arm/Gstep.c

@@ -268,5 +268,5 @@ unw_step (unw_cursor_t *cursor)
             }
         }
     }
-  return ret == -UNW_ENOINFO ? 0 : 1;
+  return ret == -UNW_ENOINFO ? 0 : ret;
 }