fpga: region: use dev_err instead of pr_err

Use dev_err messages instead of pr_err.

Also s/&region->dev/dev/ in two places where we already
have dev = &region->dev.

Signed-off-by: Alan Tull <atull@kernel.org>
Acked-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>