serial: 8250: omap: Don't skip resource freeing if pm_runtime_resume_and_get() failed

In the Linux kernel, the following vulnerability has been resolved:

serial: 8250: omap: Don't skip resource freeing if pm_runtime_resume_and_get() failed

Returning an error code from .remove() makes the driver core emit the

little helpful error message:

remove callback returned a non-zero value. This will be ignored.

and then remove the device anyhow. So all resources that were not freed

are leaked in this case. Skipping serial8250_unregister_port() has the

potential to keep enough of the UART around to trigger a use-after-free.

So replace the error return (and with it the little helpful error

message) by a more useful error message and continue to cleanup.