drivers: clk: Adjust temp var data type to properly match that of struct clk_ops

In commit 5c5992cb ("clk: Add debugging for return values"), a
temporary storage variable was added around the ops->get_rate() call
inside clk_get_rate(), so that the result could be passed through
log_ret.

This temporary variable was declared as an int, yet when we look in
struct clk_ops, we can see this needs to be a ulong:
ulong (*get_rate)(struct clk *clk);

This was resulting in a signed to unsigned casting error on our
builds, where a clock value of 0xABCDABCD was being incorrectly cast
to 0xFFFFFFFFABCDABCD.

Signed-off-by: Nathan Barrett-Morrison <nathan.morrison@timesys.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
Link: https://lore.kernel.org/r/20230515195005.1961495-1-nathan.morrison@timesys.com