cifs: convert case-insensitive dentry ops to use new case conversion routines

cifs: convert case-insensitive dentry ops to use new case conversion routines

Have the case-insensitive d_compare and d_hash routines convert each
character in the filenames to wchar_t's and then use the new
cifs_toupper routine to convert those into uppercase.

With this scheme we should more closely emulate the case conversion that
the servers will do.

Reported-and-Tested-by: Jan-Marek Glogowski <glogow@fbihome.de>
Signed-off-by: Jeff Layton <jlayton@redhat.com>