Convert (ffs(val) - 1) to ctz32(val)

Convert (ffs(val) - 1) to ctz32(val)

This commit was generated mechanically by coccinelle from the following
semantic patch:

@@
expression val;
@@
- (ffs(val) - 1)
+ ctz32(val)

The call sites have been audited to ensure the ffs(0) - 1 == -1 case
never occurs (due to input validation, asserts, etc).  Therefore we
don't need to worry about the fact that ctz32(0) == 32.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1427124571-28598-5-git-send-email-stefanha@redhat.com
Signed-off-by: Kevin Wolf <kwolf@redhat.com>