media: ti: Use devm_platform_ioremap_resource() in ti_csi2rx_probe()

A wrapper function is available since the commit 7945f929
("drivers: provide devm_platform_ioremap_resource()").

* Thus reuse existing functionality instead of keeping duplicate source
  code.

* Delete a local variable which became unnecessary with this refactoring.

This issue was transformed by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Jai Luthra <j-luthra@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>