fpga: region: Drop unneeded part due to merge issue

This part is removed in upstream commit 8886a579 ("fpga: region:
Use standard dev_release for class driver), but introduced when merging.
So we should drop it.

Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>