ASoC: msm: Null dereference check added

In asm_read function we should check buffer pointer
before it is dererferenced.

CRs-Fixed: 612682
Change-Id: I1968c038e1d35381bf174000287d542441e41092
Signed-off-by: Anish Kumar <kanish@codeaurora.org>
diff --git a/sound/soc/msm/qdsp6v2/q6asm.c b/sound/soc/msm/qdsp6v2/q6asm.c
index badc3c3..48bf2f4 100644
--- a/sound/soc/msm/qdsp6v2/q6asm.c
+++ b/sound/soc/msm/qdsp6v2/q6asm.c
@@ -3748,6 +3748,11 @@
 		mutex_lock(&port->lock);
 
 		dsp_buf = port->dsp_buf;
+		if (port->buf == NULL) {
+			pr_err("%s buf is NULL\n", __func__);
+			mutex_unlock(&port->lock);
+			return -EINVAL;
+		}
 		ab = &port->buf[dsp_buf];
 
 		pr_debug("%s:session[%d]dsp-buf[%d][%p]cpu_buf[%d][%p]\n",