This fixes filename case handling in vfat_revalidate():

before:
	# mount -t vfat /dev/hda6 /mnt -o shortname=winnt
	# cd /mnt
	# cat File.Txt			# make negative dentry
	cat: File.Txt: No such file or directory
	# touch file.txt		# match negative dentry
	# ls
	File.Txt

after:
	# mount -t vfat /dev/hda6 /mnt -o shortname=winnt
	# cd /mnt
	# cat File.Txt			# make negative dentry
	cat: File.Txt: No such file or directory
	# touch file.txt		# match negative dentry
	# ls
	file.txt