of: spmi: Remove excessive loop in dev-container traversal

This factors out some code that is executed twice for no reason.

Change-Id: I562f41b05656dc6d8621859ef5b598869a61c28e
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>