drm: msm: sde: fix the node name for sde register dump

Reg dma registers were being dumped as vbif_nrt registers due to
incorrect name being passed to the register function. Change updates the
name to reg_dma.

Change-Id: I19e98bafb0ec9eee1334a039f1aed816d609877d
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>