i2c: designware: suppress unneeded SDA hold time warnings

The hardware may not support SDA hold time configuration, but if it is
not set in the Device Tree either, there is no need to print a warning.

Reported-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>