[media] v4l: vb2-memops: use vma slab when vma allocation
[media] v4l: vb2-memops: use vma slab when vma allocation

The slab for vm_area_struct which is vm_area_cachep is already prepared
for the general use. Instead of kmalloc() for the vma copy for userptr,
allocation from vm_area_cachep is more beneficial.

CC: Hans Verkuil <3a513708f73c27e7d36ebc496aa41dad6a3153ea@cisco.com>
CC: Laurent Pinchart <3ded2f39a78f0d7044839546f95841842b4d7c96@ideasonboard.com>
Signed-off-by: Cho KyongHo <85e547a6ca510a81af12a94f261b0997900ebcc5@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <ad86ba2154032c9f55743a190faa2459a9d61d42@osg.samsung.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs