ALSA: core: pcm_memory: dereference pointer after NULL checks

Fix cppcheck warnings:

sound/core/pcm_memory.c:380:26: warning: Either the condition
'!substream' is redundant or there is possible null pointer
dereference: substream. [nullPointerRedundantCheck]
 struct snd_card *card = substream->pcm->card;
                         ^
sound/core/pcm_memory.c:384:6: note: Assuming that condition
'!substream' is not redundant
 if (PCM_RUNTIME_CHECK(substream))
     ^
sound/core/pcm_memory.c:380:26: note: Null pointer dereference
 struct snd_card *card = substream->pcm->card;
                         ^
sound/core/pcm_memory.c:433:26: warning: Either the condition
'!substream' is redundant or there is possible null pointer
dereference: substream. [nullPointerRedundantCheck]
 struct snd_card *card = substream->pcm->card;
                         ^
sound/core/pcm_memory.c:436:6: note: Assuming that condition
'!substream' is not redundant
 if (PCM_RUNTIME_CHECK(substream))
     ^
sound/core/pcm_memory.c:433:26: note: Null pointer dereference
 struct snd_card *card = substream->pcm->card;
                         ^
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200902212133.30964-4-pierre-louis.bossart@linux.intel.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_memory.c

@@ -377,7 +377,7 @@ struct page *snd_pcm_sgbuf_ops_page(struct snd_pcm_substream *substream, unsigne
  */
 int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t size)
 {
-	struct snd_card *card = substream->pcm->card;
+	struct snd_card *card;
 	struct snd_pcm_runtime *runtime;
 	struct snd_dma_buffer *dmab = NULL;
 
@@ -387,6 +387,7 @@ int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t size)
 		       SNDRV_DMA_TYPE_UNKNOWN))
 		return -EINVAL;
 	runtime = substream->runtime;
+	card = substream->pcm->card;
 
 	if (runtime->dma_buffer_p) {
 		/* perphaps, we might free the large DMA memory region