[media] v4l: vb2-dma-contig: fix vb2_get_vma()

[media] v4l: vb2-dma-contig: fix vb2_get_vma()

nvmap expects that same VMA is opened and closed to disallow
memory leaks. So, nvmap panics if a previously non-existent vma
is being closed through it.

Hence modify the sequence in vb2_get_vma() to
open the vma_copy before returning it. This way nvmap sees that
the vma_copy exists in its list and will close the vma.

Bug 200164002

Change-Id: I45dfb8ca710375a0e70d9802ebdcc9fd4d0b4600
Signed-off-by: Sri Krishna chowdary <schowdary@nvidia.com>
Reviewed-on: http://git-master/r/931997
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Frank Shi <fshi@nvidia.com>
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>