i2c: Force DLL0945 touchpad i2c freq to 100khz

This patch fixes an issue where the touchpad cursor movement becomes
slow on the Dell Precision 5560. Force the touchpad freq to 100khz
as a workaround.

Tested on Dell Precision 5560 with 6.14 to 6.14.6. Cursor movement
is now smooth and responsive.

Signed-off-by: fangzhong.zhou <myth5@myth5.com>
[wsa: kept sorting and removed unnecessary parts from commit msg]
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>