gma500: remove annoying deprecation warning

In commit e4570897 ("drm/dp-helper: Move the legacy helpers to
gma500") the legacy i2c helpers were moved to the only remaining user of
them, the gma500 driver.  Together with that move, i2c_dp_aux_add_bus()
was marked deprecated and started warning about its remaining use.

It's now been a year and a half of annoying warning, and apparently
nobody cares enough about gma500 to try to move it along to the more
modern models.

Get rid of the warning - if even the gma500 people don't care enough,
then they should certainly not spam other innocent developers with a
warning that might hide other, much more real issues.

Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>