drivers: i2c: stm32: sync stm32_v2 RTIO on PM runtime state

Always call pm_device_runtime_get() when registering a target
even if the device is not wakeup capable to prevent I2C target not being
function if the device goes into a SoC Stop mode.

This change ports into the STM32 v2 RTIO driver the change made in the
non-RTIO driver through commit 67f80e35 ("i2c: stm32: always call
runtime_get when registering targets").

Signed-off-by: Etienne Carriere <etienne.carriere@st.com>