hfsplus: fix option parsing during remount

hfsplus only actually uses the force option during remount, but it uses
the full option parser with a fake superblock to do so.  This means remount
will fail if any nls option is set (which happens frequently with older
mount tools), even if it is the same.

Fix this by adding a simpler version of the parser that only parses the force
option for remount.

Signed-off-by: Christoph Hellwig <hch@tuxera.com>