ASoC: Intel: atom: remove static analysis false positive

ASoC: Intel: atom: remove static analysis false positive

make KCFLAGS='-fanalyzer' sound/soc/intel/atom/ reports a possible
NULL pointer dereference.

sound/soc/intel/atom/sst/sst_stream.c:221:40: error: dereference of
NULL ‘block’ [CWE-476] [-Werror=analyzer-null-dereference]
  221 |                         unsigned char *r = block->data;

This is a false-positive, the GCC analyzer generated that report by
considering if (bytes->block) as true in some cases and false in
others.

We can simplify the code and use a local variable so that static
analysis does not try to look for cases where bytes->block can be
modified concurrently.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Yaochun Hung <yc.hung@mediatek.com>
Link: https://lore.kernel.org/r/20230731213748.440285-8-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>