firmware: microchip: fix incorrect error report of programming:timeout on success

After successfully programming the SPI flash with an MFPS auto update
image, the error sysfs attribute reports programming:timeout.
This is caused by an incorrect check on the return value from
wait_for_completion_timeout() in mpfs_auto_update_poll_complete().

Fixes: ec5b0f11 ("firmware: microchip: add PolarFire SoC Auto Update support")
Signed-off-by: Steve Wilkins <steve.wilkins@raymarine.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>