i2c: npcm7xx: Fix callback completion ordering

Sometimes, our completions race with new master transfers and override
the bus->operation and bus->master_or_slave variables. This causes
transactions to timeout and kernel crashes less frequently.

To remedy this, we re-order all completions to the very end of the
function.

Fixes: 56a1485b

 ("i2c: npcm7xx: Add Nuvoton NPCM I2C controller driver")
Signed-off-by: William A. Kennington III <william@wkennington.com>
Reviewed-by: Tali Perry <tali.perry1@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>