hw/nvme: clean up confusing use of errp/local_err

hw/nvme: clean up confusing use of errp/local_err

Remove an unnecessary local Error value in nvme_realize(). In the
process, change nvme_check_constraints() to return a bool.

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
(cherry picked from commit 784fd35387e9e6b42e3f365ddf44263eb25de8f7)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: needed for v8.2.0-2319-gfa905f65c5
 "hw/nvme: add machine compatibility parameter to enable msix exclusive bar")