HAL_ChibiOS: fix sdcard param init

the write was failing because of a 0 byte write attempt, the response was -1 vs 0
this results in not using the sdcard backend for storage for all boots after the initial

libraries/AP_HAL_ChibiOS/Storage.cpp

@@ -103,7 +103,7 @@ void Storage::_storage_open(void)
             }
             // pre-fill to full size
             if (AP::FS().lseek(log_fd, ret, SEEK_SET) != ret ||
-                AP::FS().write(log_fd, &_buffer[ret], CH_STORAGE_SIZE-ret) != CH_STORAGE_SIZE-ret) {
+                (CH_STORAGE_SIZE-ret > 0 && AP::FS().write(log_fd, &_buffer[ret], CH_STORAGE_SIZE-ret) != CH_STORAGE_SIZE-ret)) {
                 ::printf("setup failed for " HAL_STORAGE_FILE "\n");
                 AP::FS().close(log_fd);
                 log_fd = -1;