i2c: designware: Drop hard coded FIFO depth assignment

It's not clear why the commit fe20ff5c
  ("i2c-designware: Add support for Designware core behind PCI devices.")
followed by commit b61b1415
  ("i2c-designware: add support for Intel Lynxpoint")
chose to hard code FIFO depth size. The FIFO depth on all hardware,
I have tested on, can be nicely detected automatically.

Thus, we may safely drop hard coded FIFO sizes from 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@kernel.org>