nvme: Return negative error value for internal errors

nvme: Return negative error value for internal errors

To support the mapping of error values which will be introduced in the
next patches, All the internal errors caused in the middle of the
subcommands preparation or teardown should be returned as a negative
value to make it distinguished from nvme error status which is positive.

This patch makes all the internal error values which used to be returned
as a positive value to be returned as a negative value.

Cc: Keith Busch <kbusch@kernel.org>
Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>