mmc: sdhci: Use regulator min/max voltage range according to spec

For regulator vmmc/vmmcq, use voltage range as below
3.3v/3.0v: (2.7v, 3.6v)
1.8v: (1.7v, 1.95v)
Original code uses the precise value which may fail in regulator
driver if it does NOT support the precise voltage.

Signed-off-by: Jialing Fu <jlfu@marvell.com>
Signed-off-by: Kevin Liu <kliu5@marvell.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>