(tidy)driver_buses: fix unused variable error

Previously, the `cppcheck` tool reported an error in the `start_buses`
function of `buses.c` due to the structure of its macro definitions. The
goal was to initialize a value to capture the return state when
initializing various buses on the host. If a bus (FOO) was exposed
through a macro set by Kconfig, an attempt would be made to initialize
the FOO bus. If the attempt failed, the `start_buses` function would
immediately return the ESP32 error status from FOO. If the attempts
succeeded, `start_buses` would return a static definition of "ESP_OK."

However, the use of macros by the compiler's preprocessor introduced
non-determinism for static analysis tools, leading to ambiguity
regarding the use of `res`.

This commit slightly changes the behavior by initializing `res` to the
desired resulting value, "ESP_OK," and returning `res` instead of
"ESP_OK." If any of the buses fail to initialize, the value of `res`
will be overwritten, after which the behavior will remain the same.

Author: brianredbeard

components/buses/buses.c

@@ -27,7 +27,7 @@ static xSemaphoreHandle i2c1_mux = NULL;
 
 esp_err_t start_buses() {
     // This function initializes the VSPI, HSPI and I2C buses of the ESP32
-    esp_err_t res;
+    esp_err_t res = ESP_OK;
 
     #ifdef CONFIG_BUS_VSPI_ENABLE
         spi_bus_config_t vspiBusConfiguration = {0};
@@ -109,7 +109,7 @@ esp_err_t start_buses() {
         if (i2c1_mux == NULL) return ESP_ERR_NO_MEM;
     #endif
 
-    return ESP_OK;
+    return res;
 }
 
 /* I2C helper functions */