The V4L2 documentation says that applications must call the VIDIOC_REQBUFS
ioctl to determine if a memory mapped, user pointer or DMABUF based I/O is
supported by the driver.

For example GStreamer does this by first calling VIDIOC_REQBUFS with count
zero for all the possible streaming I/O methods and then finally doing the
real VIDIOC_REQBUFS with count N using a known to be supported memory type.

But the driver prints an error on VIDIOC_REQBUFS if the memory type is not
supported which leads to the following errors that can confuse the users:

[  178.704390] vidioc_reqbufs:575: Only V4L2_MEMORY_MMAP is supported
[  178.704666] vidioc_reqbufs:575: Only V4L2_MEMORY_MMAP is supported
[  178.714956] vidioc_reqbufs:575: Only V4L2_MEMORY_MMAP is supported
[  178.715229] vidioc_reqbufs:575: Only V4L2_MEMORY_MMAP is supported
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>