arm: mvebu: spl: Fix parsing SDIO kwbimage

Despite the official specification, Marvell BootROM does not interpret
srcaddr from SDIO image as offset in number of sectors (like for SATA
image), but as offset in bytes (like for all other images except SATA).

To process SDIO kwbimage and load U-Boot proper from it in the same way as
Marvell BootROM, it is needed to interpret srcaddr in bytes. This change
fixes booting of U-Boot proper from SPL code stored in SDIO image.

Fixes: 2226ca17 ("arm: mvebu: Load U-Boot proper binary in SPL code based on kwbimage header")
Signed-off-by: Pali Rohár <pali@kernel.org>