drm: drop i2c subdir from Makefile

drm: drop i2c subdir from Makefile

The commit 325ba852d148 ("drm/i2c: move TDA998x driver under
drivers/gpu/drm/bridge") deleted the drivers/gpu/drm/i2c/ subdir, but
didn't update upper level Makefile. Drop corresponding line to fix build
issues.

Fixes: 325ba852d148 ("drm/i2c: move TDA998x driver under drivers/gpu/drm/bridge")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/dri-devel/20250213113841.7645b74c@canb.auug.org.au
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250213-fix-tda-v1-1-d3d34b2dc907@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>