ublk: Fix signedness bug returning warning

There are two warnings reported by smatch:

drivers/block/ublk_drv.c:445 ublk_setup_iod_zoned() warn:
	signedness bug returning '(-95)'
drivers/block/ublk_drv.c:963 ublk_setup_iod() warn:
	signedness bug returning '(-5)'

The type of "blk_status_t" is either be a u32 or u8, but this two
functions return a negative value when not supported or failed. Use
the error code of the blk module to fix these warnings.

Fixes: 29802d7c

 ("ublk: enable zoned storage support")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202308100201.TCRhgdvN-lkp@intel.com/
Signed-off-by: Li Zetao <lizetao1@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230810084836.3535322-1-lizetao1@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>