media: ngene: move the tsin_exchange() stripcopy block into a function

Move the copy logic that will skip previously inserted TS NULL frames when
moving data to the DVB ring buffers into an own function. This is done to
not duplicate code all over the place with the following TS offset shift
fixup patch.

While we're touching this part of the code, get rid of the DEBUG_CI_XFER
debug-ifdeffery. This could be toggleable either by a Kconfig or a module
param, but in the end this will accidentally be enabled and cause lots
of kernel log messages, and such devel debug shouldn't be there anyway.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>