msm: ADSPRPC: Validate rpra to avoid Null pointer dereference

In get_args function their is no NULL pointer check for rpra 
variable, that might lead to null pointer dereference. Add 
condition to verify.

Change-Id: I0789e8ea875221de5809598419bc7f842aa3e22e
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>
diff --git a/drivers/char/adsprpc.c b/drivers/char/adsprpc.c
index 3f35d54..4935b6e 100644
--- a/drivers/char/adsprpc.c
+++ b/drivers/char/adsprpc.c
@@ -1381,7 +1381,7 @@
 	/* copy non ion buffers */
 	PERF(ctx->fl->profile, GET_COUNTER(perf_counter, PERF_COPY),
 	rlen = copylen - metalen;
-	for (oix = 0; oix < inbufs + outbufs; ++oix) {
+	for (oix = 0; rpra && oix < inbufs + outbufs; ++oix) {
 		int i = ctx->overps[oix]->raix;
 		struct fastrpc_mmap *map = ctx->maps[i];
 		size_t mlen;
@@ -1432,7 +1432,7 @@
 		if (map && (map->attr & FASTRPC_ATTR_COHERENT))
 			continue;
 
-		if (rpra[i].buf.len && ctx->overps[oix]->mstart)
+		if (rpra && rpra[i].buf.len && ctx->overps[oix]->mstart)
 			dmac_flush_range(uint64_to_ptr(rpra[i].buf.pv),
 			uint64_to_ptr(rpra[i].buf.pv + rpra[i].buf.len));
 	}