Fix writing sector 0 as the first write.

This was the FS issue I saw when debugging wifi and only happens
when the first write is to sector 0. It causes issues because it
blanks all of sector 0 after the first block.

Fixes #3133

Author: tannewt

ports/esp32s2/supervisor/internal_flash.c

@@ -43,10 +43,16 @@
 
 STATIC const esp_partition_t * _partition;
 
+// TODO: Split the caching out of supervisor/shared/external_flash so we can use it.
+#define SECTOR_SIZE 4096
+STATIC uint8_t _cache[SECTOR_SIZE];
+STATIC uint32_t _cache_lba;
+
 void supervisor_flash_init(void) {
     _partition = esp_partition_find_first(ESP_PARTITION_TYPE_DATA,
                                           ESP_PARTITION_SUBTYPE_DATA_FAT,
                                           NULL);
+    _cache_lba = 0xffffffff;
 }
 
 uint32_t supervisor_flash_get_block_size(void) {
@@ -61,11 +67,6 @@ void port_internal_flash_flush(void) {
 
 }
 
-// TODO: Split the caching out of supervisor/shared/external_flash so we can use it.
-#define SECTOR_SIZE 4096
-STATIC uint8_t _cache[SECTOR_SIZE];
-STATIC uint32_t _cache_lba;
-
 mp_uint_t supervisor_flash_read_blocks(uint8_t *dest, uint32_t block, uint32_t num_blocks) {
     esp_partition_read(_partition,
                        block * FILESYSTEM_BLOCK_SIZE,