HSI: omap_ssi_port: Drop error checking for debugfs_create_dir

This patch fixes the error checking in omap_ssi_port.c. The DebugFS
kernel API is developed in a way that the caller can safely ignore the
errors that occur during the creation of DebugFS nodes.

Signed-off-by: Osama Muhammad <osmtendev@gmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>