getinfo_super1: Use MaxSector in place of sb->size

getinfo_super1: Use MaxSector in place of sb->size

when deciding whether the array is clean or dirty, compare
sb->resync_offset against MaxSector and not against sb->size

With RAID6 resyncing and subsequent drive failures, it is possible to
reach the case, in which sb->resync_offset==sb->size. This happens
when resync is aborted due to drive failures, and immediately a
rebuild of a spare starts. In this case, mdadm was considered the
array as clean, while kernel was considering the array as dirty. It is
better for mdadm also to consider the array as dirty in this case.

Signed-off-by: NeilBrown <neilb@suse.de>