OMAPDSS: Remove kfree for memory allocated with devm_kzalloc

It's not necessary to free memory allocated with devm_kzalloc
in a remove function and using kfree leads to a double free.

Signed-off-by: Emil Goode <emilgoode@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>