mmc: sdhci: fix bus width switching on Samsung SoCs

Fix bus width switching from 8-bit mode down to 4-bit or 1-bit modes on
Samsung SoCs using SDHCI_QUIRK_USE_WIDE8.  These SoCs report controller
version 2.0 yet they support 8-bit bus widths.  If 8-bit mode was
previously enabled and then an operation like "mmc dev" caused a switch
back down to 4-bit or 1-bit mode, WIDE8 was left set, causing failures.

This problem was manifested by "mmc dev" timing out.

Signed-off-by: Matt Reimer <mreimer@sdgsystems.com>