Ensure 64bit math for SD card FSInfo

[earlephilhower]

Fixes #1552

Ensure that 64 bit multiplication is done when calculating the total size available and used for SDFS.

[LinusHeu]

It works for me.
Before (master):

After (sd1):

#include <Arduino.h>
#include <SDFS.h>

void setup() {
  Serial.begin();
  while(!Serial);
  delay(1000);
  Serial.println("Hallo");

  SDFSConfig sdconf;
  sdconf.setCSPin(17);
  //SPI.setCS(17);
  SPI.setRX(16);
  SPI.setTX(19);
  SPI.setSCK(18);
  SDFS.setConfig(sdconf);
  Serial.println(SDFS.begin());
  FSInfo64 fsinfo;
  SDFS.info64(fsinfo);
  Serial.println(fsinfo.totalBytes);
  Serial.println(fsinfo.usedBytes);
  
}

void loop() {
  // put your main code here, to run repeatedly:
}

[earlephilhower]

Thanks, @LinusHeu !