ARM: davinci: dm644x: improve readability using macro

Replace the VPSS base address "magic number" with the
define "DM644X_VPSS_BASE" to improve readability.

While at it, fix the indentation done using spaces in
this part of code.

Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>