rtio: Release sqe before submitting cqe
rtio: Release sqe before submitting cqe

When an application is waiting on a completion it may be expecting,
rightfully so, that a new submissions slot is available.

Frees the submission queue event prior to enqueuing
the completion queue event in the simple executor.

Signed-off-by: Tom Burdick <63c280986e32082c9e27a1a69ac8b19e3d0c6b4b@intel.com>

zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr