spi: stm32-ospi: Use of_reserved_mem_region_to_resource() for "memory-region"

Use the newly added of_reserved_mem_region_to_resource() function to
handle "memory-region" properties.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20250709021638.2047365-1-robh@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>