dma-buf: DMABUF_DEBUG should depend on DMA_SHARED_BUFFER

DMA-BUF debug checks are an option of DMA-BUF.  Enabling DMABUF_DEBUG
without DMA_SHARED_BUFFER does not have any impact, as drivers/dma-buf/
is not entered during the build when DMA_SHARED_BUFFER is disabled.

Fixes: 84335675 ("dma-buf: Add debug option")
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/20210902124913.2698760-3-geert@linux-m68k.org