drm/msm/dsi-staging: fix issues related to deferral

Fix two issues in dsi_display interfering with probe deferral:
clear clock pointer when they fail to initialize, and remove
debug_fs entries recursively.

Change-Id: Ide542cef7f82b6f5caa52ad4c3da6662b8ae58fc
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>