arm64: mvebu: Update bubt command MMC block device access

Update the MMC block device access code in bubt command
implementation according to the latest MMC driver changes.

Change-Id: Ie852ceefa0b040ffe1362bdb7815fcea9b2d923b
Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Neta Zur Hershkovits <neta@marvell.com>
Cc: Omri Itach <omrii@marvell.com>
Cc: Igal Liberman <igall@marvell.com>
Cc: Haim Boot <hayim@marvell.com>
Cc: Hanna Hawa <hannah@marvell.com>