media: staging: atomisp: Remove Gmin dead code #2

media/lm3642.h is not used anywhere. Moreover, there is a driver under
LEDs framework for very same IP which would be used anyway.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>