i2c: designware: Drop unneeded condition in i2c_dw_validate_speed()

We may bailout directly from the loop instead of breaking it and
testing a loop counter. This also gives advantages such as decreased
indentation level along with dropped unneeded condition.

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@kernel.org>