mei: free read cb on ctrl_wr list flush

There is a little window during disconnection flow
when read cb is moved between lists and may be not freed.
Remove moving read cbs explicitly during flash fixes this memory
leak.

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>