V4L/DVB (12108): v4l2-i2c-drv.h: add comment describing when not to use this header.

Make it very clear that this header should not be used for i2c drivers that
do not need to be compiled for pre-2.6.26 kernels.

As soon as the minimum supported kernel in the v4l-dvb repository becomes
2.6.26 or up, then this header should be removed entirely.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

include/media/v4l2-i2c-drv.h

@@ -22,7 +22,7 @@
  */
 
 /* NOTE: the full version of this header is in the v4l-dvb repository
- * and allows v4l i2c drivers to be compiled on older kernels as well.
+ * and allows v4l i2c drivers to be compiled on pre-2.6.26 kernels.
  * The version of this header as it appears in the kernel is a stripped
  * version (without all the backwards compatibility stuff) and so it
  * looks a bit odd.
@@ -30,6 +30,9 @@
  * If you look at the full version then you will understand the reason
  * for introducing this header since you really don't want to have all
  * the tricky backwards compatibility code in each and every i2c driver.
+ *
+ * If the i2c driver will never be compiled for pre-2.6.26 kernels, then
+ * DO NOT USE this header! Just write it as a regular i2c driver.
  */
 
 #ifndef __V4L2_I2C_DRV_H__