OMAP2+: smartreflex: remove SR debug directory in omap_sr_remove()

omap_sr_probe() creates the smartreflex debug directory and its
underlying nvalue debug directory. These directories are removed in
omap_sr_remove().

Basic smartreflex functionality tested on OMAP3630 Zoom3 & OMAP4430 SDP

Signed-off-by: Anand S Sawant <sawant@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>