accel/ivpu: Fix general protection fault in ivpu_bo_list()

Check if ctx is not NULL before accessing its fields.

Fixes: 37dee2a2 ("accel/ivpu: Improve buffer object debug logs")
Cc: stable@vger.kernel.org # v6.8
Reviewed-by: Karol Wachowski <karol.wachowski@intel.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241210130939.1575610-2-jacek.lawrynowicz@linux.intel.com