switchtec: Remove immediate status check after submitting MRPC command

After submitting a Firmware Download MRPC command, Switchtec firmware will
delay Management EP BAR MemRd TLP responses by more than 10ms.  This is a
firmware limitation.  Delayed MemRd completions are a problem for systems
with a low Completion Timeout (CTO).

The current driver checks the MRPC status immediately after submitting an
MRPC command, which results in a delayed MemRd completion that may cause a
Completion Timeout.

Remove the immediate status check and rely on the check after receiving an
interrupt or timing out.

This is only a software workaround to the READ issue and a proper fix of
this should be done in firmware.

Fixes: 080b47de ("MicroSemi Switchtec management interface driver")
Signed-off-by: Kelvin Cao <kelvin.cao@microchip.com>
Signed-off-by: Wesley Sheng <wesley.sheng@microchip.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>