i2c: designware: Don't warn about missing get_clk_rate_khz

i2c: designware: Don't warn about missing get_clk_rate_khz

Converting the WARN_ON() to a dev_dbg() message in
i2c_dw_clk_rate().

That removes the need to supply a dummy implementation for
the callback (or alternatively a dummy clk device) when the
fallback path is preferred where the existing values already
in the clock registers are used - when a firmware has
programmed the clock registers.

The fallback path was introduced in commit 4fec76e0985c
("i2c: designware: Fix wrong setting for {ss,fs,hs}_{h,l}cnt
registers").

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Link: https://lore.kernel.org/r/20250513124015.2568924-1-heikki.krogerus@linux.intel.com
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>