sunhme: fix an IS_ERR() vs NULL check in probe

The devm_request_region() function does not return error pointers, it
returns NULL on error.

Fixes: 914d9b27 ("sunhme: switch to devres")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
Link: https://lore.kernel.org/r/Y0bWzJL8JknX8MUf@kili


Signed-off-by: Jakub Kicinski <kuba@kernel.org>