staging: sm750fb: use BIT macro for I2C_CTRL fields

Replace complex definition of I2C_CTRL register fields with BIT() macro and
use open-coded implementation for register manipulation

Signed-off-by: Mike Rapoport <mike.rapoport@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>