ObjectCacher::_wait_for_write(): init 'bool done'

ObjectCacher::_wait_for_write(): init 'bool done'

Init 'bool done' with 'false' to fix:

osdc/Objecter.h:915:27: warning: implicit conversion los: variable 'done'
 may be uninitialized when used here [-Wconditional-uninitialized]
      while (!done)
              ^~~~
osdc/ObjectCacher.cc:1399:14: note: initialize the variable 'done' to
 silence this warning
    bool done;
             ^
              = false

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>