i2c: ibm_iic: rename i2c_timings struct due to clash with generic version

Fixes: e1dba01c ("i2c: add generic routine to parse DT for timing information")
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>