Revert "i2c: jz4780: prevent potential division by zero"

This reverts commit 34cf2acd. 'ret' is
not set when bailing out. Also, there is a better place to check for 0.

Reported-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>