ASoC: Intel: Skylake: Fix the NULL pointer exception in dsp_clean up

If request firmware fails at init, the code loader DMA allocation
can be NULL, so check for boot complete before freeing up these
resources

Signed-off-by: Dharageswari R <dharageswari.r@intel.com>
Signed-off-by: Jeeja KP <jeeja.kp@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>