dma-buf: DMABUF_SYSFS_STATS should depend on DMA_SHARED_BUFFER

DMA-BUF sysfs statistics are an option of DMA-BUF.  It does not make
much sense to bother the user with a question about DMA-BUF sysfs
statistics if DMA-BUF itself is not enabled.  Worse, enabling the
statistics enables the feature.

Fixes: bdb8d06d ("dmabuf: Add the capability to expose DMA-BUF stats in sysfs")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210902124913.2698760-4-geert@linux-m68k.org