i2c: generic recovery: check SCL before SDA

Move the check for a stuck SCL before the check for a high SDA.
This prevent false positives in the specific case that SDA is fine
and SCL is stuck, which previously returned 0.

Also check SDA again after the loop, if we can.
Together, these changes should lead to a lot more failed
recoveries being caught and returning error codes.

Signed-off-by: Claudio Foellmi <claudio.foellmi@ergon.ch>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>