rename function to avoid confusion

Author: jepler

ports/espressif/supervisor/port.c

@@ -95,7 +95,7 @@
 #define esp_himem_reserved_area_size() (0)
 #endif
 
-static size_t spiram_size_usable_for_malloc(void) {
+static size_t spiram_size_usable(void) {
     /* SPIRAM chip may be larger than the size we can map into address space */
     size_t s = MIN(esp_spiram_get_size(), SOC_EXTRAM_DATA_SIZE);
     return s - esp_himem_reserved_area_size();
@@ -220,7 +220,7 @@ safe_mode_t port_init(void) {
 
     #ifdef CONFIG_SPIRAM
     if (esp_spiram_is_initialized()) {
-        size_t spiram_size = spiram_size_usable_for_malloc();
+        size_t spiram_size = spiram_size_usable();
         #ifdef CONFIG_IDF_TARGET_ESP32
         heap = (uint32_t *)SOC_EXTRAM_DATA_LOW;
         #else