At least on SPARC, if MSI/MSI-X isn't supported, we get EINVAL if
we ask for more than one vector. This isn't covered by our ENOSPC
check.

If we get EINVAL, decrease our ask to just one vector, instead of
bailing out in error.

Fixes: 3b6592f7 ("nvme: utilize two queue maps, one for reads and one for writes")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jens Axboe <axboe@kernel.dk>