PCI: imx6: Add speed change timeout message

Currently, the timeout is never detected as count has a value of -1 if a
timeout happens, but the code is checking for 0.  Also, this patch removes
the unneeded final wait if a timeout occurs.

[bhelgaas: reworked starting from http://lkml.kernel.org/r/1433543864-7252-1-git-send-email-troy.kisky@boundarydevices.com]
Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>