The ADEF bits in the TSCR register have different meanings in read and
write mode. For this reason ADEF has to be reset on every
read-modify-write operation.
This patch introduces a special write function for this register, which
takes care of it.

Thanks to Holger Magnussen for pointing my nose at this problem.
Signed-off-by: Andreas Oberritter <obi@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>