dma-buf: fix resource leak on -ENOTTY error return path

Commit f9d3b2c6 upstream.

The -ENOTTY error return path does not free the allocated
kdata as it returns directly. Fix this by returning via the
error handling label err.

Addresses-Coverity: ("Resource leak")
Fixes: c02a81fb

 ("dma-buf: Add dma-buf heaps framework")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191216161059.269492-1-colin.king@canonical.com