accel/ivpu: Remove unused PLL_CONFIG_DEFAULT

This change removes the unnecessary condition, makes the code clearer,
and silences clang-tidy warning.

Reviewed-by: Lizhi Hou <lizhi.hou@amd.com>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://lore.kernel.org/r/20250808111044.328800-1-jacek.lawrynowicz@linux.intel.com