drm/msm/sde: remove extra registration of reg_dma debug region

Remove an extra registration of the reg dma region as a debug
base register address since it is already registered when the
register space is mapped with ioremap.

Change-Id: I6e749e24b4a23de3f94748c77f48fa9f2ea8d774
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>