media: tw5864: check status of tw5864_frameinterval_get

clang static analysis reports this problem

tw5864-video.c:773:32: warning: The left expression of the compound
  assignment is an uninitialized value.
  The computed value will also be garbage
        fintv->stepwise.max.numerator *= std_max_fps;
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^

stepwise.max is set with frameinterval, which comes from

	ret = tw5864_frameinterval_get(input, &frameinterval);
	fintv->stepwise.step = frameinterval;
	fintv->stepwise.min = frameinterval;
	fintv->stepwise.max = frameinterval;
	fintv->stepwise.max.numerator *= std_max_fps;

When tw5864_frameinterval_get() fails, frameinterval is not
set. So check the status and fix another similar problem.
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/pci/tw5864/tw5864-video.c

@@ -767,6 +767,9 @@ static int tw5864_enum_frameintervals(struct file *file, void *priv,
 	fintv->type = V4L2_FRMIVAL_TYPE_STEPWISE;
 
 	ret = tw5864_frameinterval_get(input, &frameinterval);
+	if (ret)
+		return ret;
+
 	fintv->stepwise.step = frameinterval;
 	fintv->stepwise.min = frameinterval;
 	fintv->stepwise.max = frameinterval;
@@ -785,6 +788,9 @@ static int tw5864_g_parm(struct file *file, void *priv,
 	cp->capability = V4L2_CAP_TIMEPERFRAME;
 
 	ret = tw5864_frameinterval_get(input, &cp->timeperframe);
+	if (ret)
+		return ret;
+
 	cp->timeperframe.numerator *= input->frame_interval;
 	cp->capturemode = 0;
 	cp->readbuffers = 2;