misc: fastrpc: fix potential fastrpc_invoke_ctx leak

fastrpc_invoke_ctx can have refcount of 2 in error path where
rpmsg_send() fails to send invoke message. decrement the refcount
properly in the error path to fix this leak.

This also fixes below static checker warning:

drivers/misc/fastrpc.c:990 fastrpc_internal_invoke()
warn: 'ctx->refcount.refcount.ref.counter' not decremented on lines: 990.

Fixes: c68cfb71 ("misc: fastrpc: Add support for context")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20200512110930.2550-1-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/fastrpc.c

@@ -904,6 +904,7 @@ static int fastrpc_invoke_send(struct fastrpc_session_ctx *sctx,
 	struct fastrpc_channel_ctx *cctx;
 	struct fastrpc_user *fl = ctx->fl;
 	struct fastrpc_msg *msg = &ctx->msg;
+	int ret;
 
 	cctx = fl->cctx;
 	msg->pid = fl->tgid;
@@ -919,7 +920,13 @@ static int fastrpc_invoke_send(struct fastrpc_session_ctx *sctx,
 	msg->size = roundup(ctx->msg_sz, PAGE_SIZE);
 	fastrpc_context_get(ctx);
 
-	return rpmsg_send(cctx->rpdev->ept, (void *)msg, sizeof(*msg));
+	ret = rpmsg_send(cctx->rpdev->ept, (void *)msg, sizeof(*msg));
+
+	if (ret)
+		fastrpc_context_put(ctx);
+
+	return ret;
+
 }
 
 static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,