i2c: i2c_atmel_sam3: tweak the transfer flow for NACK and STOP

() Fixed an issue where STOP would be sent twice when a read message
   is only 1 byte.
() Skip resetting the controller when NACK is received. This is not
   an issue with the controller, so there is no need to reset
   the controller and its state machine.
() Cosmetic changes to trim lines > 80 characters.

Change-Id: If2c3b2728b3f088f7aa1fcaa6d2303ff5c4c197d
Signed-off-by: Daniel Leung <daniel.leung@intel.com>