mfd: cros ec: spi: Fix "in progress" error signaling

For host commands that take a long time to process, cros ec can return
early by signaling a EC_RES_IN_PROGRESS result. The host must then poll
status with EC_CMD_GET_COMMS_STATUS until completion of the command.

None of the above applies when data link errors are encountered. When
errors such as EC_SPI_PAST_END are encountered during command
transmission, it usually means the command was not received by the EC.
Treating such errors as if they were 'EC_RES_IN_PROGRESS' results is
almost always the wrong decision, and can result in host commands
silently being lost.

Reported-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>