dma-buf name can be set via DMA_BUF_SET_NAME ioctl, but once set
it never gets freed.

Free it in dma_buf_release().

Fixes: bb2bb903 ("dma-buf: add DMA_BUF_SET_NAME ioctls")
Reported-by: syzbot+b2098bc44728a4efb3e9@syzkaller.appspotmail.com
Cc: Greg Hackmann <ghackmann@google.com>
Cc: Chenbo Feng <fengc@google.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Chenbo Feng <fengc@google.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191227063204.5813-1-xiyou.wangcong@gmail.com