drm/tidss: use devm_platform_ioremap_resource_byname

Use the devm_platform_ioremap_resource_byname() helper instead of
calling platform_get_resource_byname() and devm_ioremap_resource()
separately.

Signed-off-by: Wang Xiaojun <wangxiaojun11@huawei.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200917062958.2183496-1-wangxiaojun11@huawei.com