i2c-isch: Decrease delay in command completion check loop

Generally it is not needed to wait for 1 msec, the SMBus get often ready
in less than 200 usecs.

msleep(1) can wait up to 20 msecs... It has a significant impact when
there is a burst of transactions on the bus.

Signed-off-by: Olivier Sobrie <olivier@sobrie.be>
Signed-off-by: Jean Delvare <khali@linux-fr.org>