md/raid1: add error handling of read error from FailFast device

Current handle_read_error() function calls fix_read_error()
only if md device is RW and rdev does not include FailFast flag.
It does not handle a read error from a RW device including
FailFast flag.

I am not sure it is intended. But I found that write IO error
sets rdev faulty. The md module should handle the read IO error and
write IO error equally. So I think read IO error should set rdev faulty.

Signed-off-by: Gioh Kim <gi-oh.kim@profitbricks.com>
Reviewed-by: Jack Wang <jinpu.wang@profitbricks.com>
Signed-off-by: Shaohua Li <shli@fb.com>