i2c: i2c-cdns: No need for dedicated probe function

The generic probe code in dm works, so get rid of the leftover cruft.

Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: u-boot@lists.denx.de