dpll: fix return value check for kmemdup

The return value of kmemdup() is dst->freq_supported, not
src->freq_supported. Update the check accordingly.

Fixes: 830ead5f

 ("dpll: fix pin dump crash for rebound module")
Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240513032824.2410459-1-nichen@iscas.ac.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>