accel/ivpu: Return max freq for DRM_IVPU_PARAM_CORE_CLOCK_RATE

accel/ivpu: Return max freq for DRM_IVPU_PARAM_CORE_CLOCK_RATE

DRM_IVPU_PARAM_CORE_CLOCK_RATE returns current NPU frequency which
could be 0 if device was sleeping. This value isn't really useful to
the user space, so return max freq instead which can be used to estimate
NPU performance.

Fixes: c39dc15191c4 ("accel/ivpu: Read clock rate only if device is up")
Cc: <stable@vger.kernel.org> # v6.7
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240402104929.941186-7-jacek.lawrynowicz@linux.intel.com