ocfs2: Tighten free bit calculation in the global bitmap

ocfs2: Tighten free bit calculation in the global bitmap

When clearing bits in the global bitmap, we do not test the current bit value.
This patch tightens the code by considering the possiblity that the bit being
cleared was already cleared.

Now this should not happen. But we are seeing stray instances in which free
bit count in the global bitmap exceeds the total bit count. In each instance
the bitmap is correct. Only the free bit count is incorrect.

This patch checks the current bit value and increments the free bit count
only if the bit was previously set. It also prints information to allow
us to debug further.

Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>