zram: remove unnecessary free

zram: remove unnecessary free

a0c516cbfc ("zram: don't grab mutex in zram_slot_free_noity") introduced
pending zram slot free in zram's write path in case of missing slot free
by memory allocation failure in zram_slot_free_notify but it is not
necessary because we have already freed the slot right before overwriting.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>