staging: wfx: fix wrong error message

The driver checks that the number of retries made by the device is
coherent with the rate policy. However, this check make sense only if
the device has returned RETRY_EXCEEDED.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191217161318.31402-11-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>