soc: microchip: mpfs: simplify error handling in mpfs_blocking_transaction()

The error handling has a kinda weird nested-if setup that is not really
adding anything. Switch it to more of an early return arrangement as a
predatory step for adding different handing for timeouts and failed
services.

Tested-by: Valentina Fernandez <valentina.fernandezalanis@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>