media: atomisp: Fix buffer overrun in gmin_get_var_int()

Not all functions used in gmin_get_var_int() update len to the actual
length of the returned string. So len may still have its initial value
of the length of val[] when "val[len] = 0;" is run to ensure 0 termination.

If this happens we end up writing one beyond the bounds of val[], fix this.

Note this is a quick fix for this since the entirety of
atomisp_gmin_platform.c will be removed once all atomisp sensor
drivers have been moved over to runtime-pm + v4l2-async device
registration.

Closes: https://lore.kernel.org/linux-media/26f37e19-c240-4d77-831d-ef3f1a4dd51d@kili.mountain/Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c

@@ -1429,8 +1429,8 @@ static int gmin_get_config_var(struct device *maindev,
 
 int gmin_get_var_int(struct device *dev, bool is_gmin, const char *var, int def)
 {
-	char val[CFG_VAR_NAME_MAX];
-	size_t len = sizeof(val);
+	char val[CFG_VAR_NAME_MAX + 1];
+	size_t len = CFG_VAR_NAME_MAX;
 	long result;
 	int ret;