mmc: sdhci: fix IS_ERR() checking of regulator_get()

There are two problems here:

The check for vmmc was printing an unnecessary pr_info() when
host->vmmc is NULL.

The intent of the check for vqmmc was to only remove UHS if we have a
regulator that doesn't support the required voltage, but since IS_ERR()
doesn't catch NULL, we were actually removing UHS modes if vqmmc isn't
present at all -- since it isn't present for most users, this breaks
UHS for them.  This patch fixes that UHS regression in 3.7-rc1.

Signed-off-by: Kevin Liu <kliu5@marvell.com>
Signed-off-by: Bin Wang <binw@marvell.com>
Reviewed-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Chris Ball <cjb@laptop.org>