i2c: iproc: Fix shifting 31 bits

Fix undefined behaviour in the iProc I2C driver by using 'BIT' marcro.

Reported-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Ray Jui <ray.jui@broadcom.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
[wsa: in commit msg, don't say 'checkpatch' but name the issue]
Signed-off-by: Wolfram Sang <wsa@kernel.org>