SNDCP: Fixup based on Coverity Scan suggestion

This commit fixes Coverity Scan defect:

CID 151900:  Null pointer dereferences  (FORWARD_NULL)
Passing null pointer "comp_field->v42bis_params->nsapi"
to "memcpy", which dereferences it.

Change-Id: Iff83e21168a267dd4b4c401ab7c603e029b3ac39
diff --git a/openbsc/src/gprs/gprs_sndcp_comp.c b/openbsc/src/gprs/gprs_sndcp_comp.c
index cae0039..1591f80 100644
--- a/openbsc/src/gprs/gprs_sndcp_comp.c
+++ b/openbsc/src/gprs/gprs_sndcp_comp.c
@@ -72,7 +72,7 @@
 	} else if (comp_field->v44_params) {
 		comp_entity->nsapi_len = comp_field->v44_params->nsapi_len;
 		memcpy(comp_entity->nsapi,
-		       comp_field->v42bis_params->nsapi,
+		       comp_field->v44_params->nsapi,
 		       sizeof(comp_entity->nsapi));
 	} else {
 		/* The caller is expected to check carefully if the all