i2c-pca: Fix waitforcompletion() return value

i2c-pca: Fix waitforcompletion() return value

commit 6abb930af064fb1cf4177d32e2c7bfb89eee0fe5 upstream.

ret is still -1, if during the polling read_byte() returns at once
with I2C_PCA_CON_SI set. So ret > 0 would lead *_waitforcompletion()
to return 0, in spite of the proper behavior.

The routine was rewritten, so that ret has always a proper value,
before returning.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Reviewed-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>