The "need_cache_flush" variable is never set to false.  When the
variable is true that means we print a warning message at the end of
the function.

Fixes: 3418d036 ("raid5-ppl: Partial Parity Log write logging implementation")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NArtur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: NShaohua Li <shli@fb.com>