i2c: designware-baytrail: baytrail_i2c_acquire() might sleep

This patch marks baytrail_i2c_acquire() that it might sleep. Also it chages
while-loop to do-while and, though it is matter of taste, gives a chance to
check one more time before report a timeout.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>