[media] V4L: soc-camera: explicitly free allocated managed memory on error

devm_kzalloc() allocations are freed when the device is unbound. But if a
certain path fails and the allocated memory cannot be used anyway it is
better to free it explicitly immediately. This patch does exactly this if
asynchronous group probing in scan_async_group() fails after memory has
been allocated.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>