dma-buf: cma_heap: Include linux/vmalloc.h to fix build failures on MIPS

We need to include <linux/vmalloc.h> in order for MIPS to find
vmap(), as it doesn't otherwise get included there.

Without this patch, one can hit the following build error:
  drivers/dma-buf/heaps/cma_heap.c: In function 'cma_heap_do_vmap':
  drivers/dma-buf/heaps/cma_heap.c:195:10: error: implicit declaration of function 'vmap'

Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Liam Mark <lmark@codeaurora.org>
Cc: Laura Abbott <labbott@kernel.org>
Cc: Brian Starkey <Brian.Starkey@arm.com>
Cc: Hridya Valsaraju <hridya@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sandeep Patil <sspatil@google.com>
Cc: Daniel Mentz <danielmentz@google.com>
Cc: Chris Goldsworthy <cgoldswo@codeaurora.org>
Cc: Ørjan Eide <orjan.eide@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Ezequiel Garcia <ezequiel@collabora.com>
Cc: Simon Ser <contact@emersion.fr>
Cc: James Jones <jajones@nvidia.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Fixes: a5d2d29e24 ("dma-buf: heaps: Move heap-helper logic into the cma_heap implementation")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201216004931.113505-1-john.stultz@linaro.org

drivers/dma-buf/heaps/cma_heap.c

@@ -20,6 +20,7 @@
 #include <linux/module.h>
 #include <linux/scatterlist.h>
 #include <linux/slab.h>
+#include <linux/vmalloc.h>
 
 
 struct cma_heap {