staging: exfat: Remove FAT/VFAT mount support, part 3

staging: exfat: Remove FAT/VFAT mount support, part 3

In this patch, we straighten out most of the cases where the
code was testing 'p_fs->vol_type == EXFAT' and '!= EXFAT'

There's still some ?: ops and a few places where the code
is doing checks for '.' and '..' that require looking at,
but those are future patches

Signed-off-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Link: https://lore.kernel.org/r/20191112211238.156490-4-Valdis.Kletnieks@vt.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>