Simplify registration using new devm_fpga_mgr_register() API.

Reviewed-by: Tom Rix <trix@redhat.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>
Link: https://lore.kernel.org/r/20201115195127.284487-7-mdf@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>