i2c: designware: Fix optional reset error handling

The commit bb475230 ("reset: make optional functions really optional")
brought a missed part of the support for an optional reset handlers.

Since that we don't need to have special error handling in the driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>