at24: Use timeout also for read

Writes may take some time on EEPROMs, so for consecutive writes, we already
have a loop waiting for the EEPROM to become ready. Use such a loop for reads,
too, in case somebody wants to immediately read after a write. Detailed bug
report and test case can be found here:

http://article.gmane.org/gmane.linux.drivers.i2c/4660

Reported-by: Aleksandar Ivanov <ivanov.aleks@gmail.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Tested-by: Aleksandar Ivanov <ivanov.aleks@gmail.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>