We need to write DW_IC_ENABLE_ENABLE (1 << 0) to the register to enable,
but instead we were writing true. This happens to work, but is quite
unusual. Make the code more readable.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>