nvmet: fix out-of-bounds access in nvmet_enable_port

nvmet: fix out-of-bounds access in nvmet_enable_port

When trying to enable a port that has no transport configured yet,
nvmet_enable_port() uses NVMF_TRTYPE_MAX (255) to query the transports
array, causing an out-of-bounds access:

[  106.058694] BUG: KASAN: global-out-of-bounds in nvmet_enable_port+0x42/0x1da
[  106.058719] Read of size 8 at addr ffffffff89dafa58 by task ln/632
[...]
[  106.076026] nvmet: transport type 255 not supported

Since commit 200adac75888, NVMF_TRTYPE_MAX is the default state as configured by
nvmet_ports_make().
Avoid this by checking for NVMF_TRTYPE_MAX before proceeding.

Fixes: 200adac75888 ("nvme: Add PCI transport type")
Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>