omap_hsmmc: fix out of bounds array access

There are 3 MMC/SD/SDIO controllers in OMAP SoCs, but only 2 structs
are defined for devices. This leads to data being written outside of
array bounds on systems that use all 3 controllers.

Update hsmmc_dev array to the correct size.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>