drivers: i2c: remove i2c master idle check

The idle status check before a i2c transfer is not a reliable
way to check whether i2c master is ready to transfer data. If
the data transfer for the previous API call is done, but, a
stop condition is not sent by the previous API, the i2c master
is not idle, but, it can start new data transfer.

Change-Id: I93dbf46cef6272f3da69a0d67fb737c9b480791f
Signed-off-by: Baohong Liu <baohong.liu@intel.com>