mvsdio: ignore high speed timing requests from the core

Empirical evidences show that this is causing far more problems than it
solves when this mode is enabled in the host hardware.  Amongst those
cards that are known to be non functional when this bit is set are:

	A-Data "Speedy" 2GB SD card
	Kodak 512MB SD card
	Ativa 1GB MicroSD card
	Marvell 8688 (WIFI/Bluetooth) SDIO card

Since those cards do work on other host controllers which do honnor the
hs timing, the issue must be with this particular host hardware.

Signed-off-by: Nicolas Pitre <nico@marvell.com>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>