media: mgb4: protect driver against spectre

Frequency range is set from sysfs via frequency_range_store(),
being vulnerable to spectre, as reported by smatch:

	drivers/media/pci/mgb4/mgb4_cmt.c:231 mgb4_cmt_set_vin_freq_range() warn: potential spectre issue 'cmt_vals_in' [r]
	drivers/media/pci/mgb4/mgb4_cmt.c:238 mgb4_cmt_set_vin_freq_range() warn: possible spectre second half.  'reg_set'

Fix it.

Fixes: 0ab1367 ("media: pci: mgb4: Added Digiteq Automotive MGB4 driver")
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Martin Tůma <martin.tuma@digiteqautomotive.com>

Author: mchehab

drivers/media/pci/mgb4/mgb4_cmt.c

@@ -227,6 +227,8 @@ void mgb4_cmt_set_vin_freq_range(struct mgb4_vin_dev *vindev,
 	u32 config;
 	size_t i;
 
+	freq_range = array_index_nospec(freq_range, ARRAY_SIZE(cmt_vals_in));
+
 	addr = cmt_addrs_in[vindev->config->id];
 	reg_set = cmt_vals_in[freq_range];