EXFAT bump version to 1.2.6 after very big update by @benpicco & @mdcasey

All changes came from here

https://github.com/benpicco/linux_exfat-staging/commits/exfat

https://github.com/mdcasey/linux_exfat-staging/commits/mdcasey

HUGE thanks to developers that made such hard work on cleaning and fixing
the code for all of exfat users :)

Great work people!