Use device life-cycle managed ioremap function to simplify probe and
exit paths.

While here add __iomem to the returned pointer to fix a sparse warning.
Signed-off-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20240212162831.67838-4-afd@ti.comSigned-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>