media: ngene: cleanup superfluous I2C adapter evaluation

Commit ee93340e ("media: ngene: deduplicate I2C adapter evaluation")
added a helper to evaluate the I2C adapter to be used for demod/tuner
attachment based on the given ngene_channel, and that helper is used in
many attach functions to initialise the i2c_adapter variable. However,
for some reason in tuner_attach_stv6110() and demod_attach_stv0900(), the
adapter evaluation wasn't removed as in all other functions. Fix (or
finalize, even) the helper use by cleaning up the superfluous I2C adapter
evaluation leftover in these two functions.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>