ARM: OMAP3+: SmartReflex: fix the use of debugfs_create_* API

The debugfs_create_* API returns a return code or NULL
in the return ptr in case of problem.
Fix the smartreflex code to take this into account.

Signed-off-by: Jean Pihet <j-pihet@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>