raid5: revert commit 11367799

Revert commit 11367799 ("md: Prevent IO hold during accessing to faulty
raid5 array") as it doesn't comply with commit c3cce6cd ("md/raid5:
ensure device failure recorded before write request returns."). That change
is not required anymore as the problem is resolved by commit 16f88949
("md: report 'write_pending' state when array in sync") - read request is
stuck as array state is not reported correctly via sysfs attribute.

Signed-off-by: Tomasz Majchrzak <tomasz.majchrzak@intel.com>
Signed-off-by: Shaohua Li <shli@fb.com>