md-cluster: check for timeout while a new disk adding

A new disk adding may end up with timeout and a new disk won't be added.
Add returning the error in that case.

Found by Linux Verification Center (linuxtesting.org) with SVACE

Signed-off-by: Denis Plotnikov <den-plotnikov@yandex-team.ru>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230925125940.1542506-1-den-plotnikov@yandex-team.ru