HSI: omap_ssi: Delete an error message for a failed memory allocation in ssi_add_controller()

The script "checkpatch.pl" pointed information out like the following.

WARNING: Possible unnecessary 'out of memory' message

Thus remove such a statement here.

Link: http://events.linuxfoundation.org/sites/events/files/slides/LCJ16-Refactor_Strings-WSang_0.pdf


Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>