block: Set memalloc_noio to false in the error path

hulk inclusion
category: bugfix
bugzilla: 188217

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In del_gendisk, memalloc_noio is set to false, so it would be better to do
the same thing in the error path.

Fixes: c6b84a94528e ("block: add error handling for device_add_disk / add_disk")
Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>
Signed-off-by: Li Nan <linan122@huawei.com>