media: bcm2835-unicam: Drop WARN on uing direct cache alias

Pi 0&1 pass all ARM accesses through the VPU L2 cache, therefore
the dma-ranges property sets the cache alias bits to other
than the direct alias, hence this WARN was firing.

It was overprotective coding, so assume that everything is OK
with the dma-ranges, and remove the WARN.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>