OMAP: PM: SmartReflex: fix potential NULL dereference

kzalloc() may fail, if so return -ENOMEM.  Also Walter Harms suggested
to use kasprintf() instead of kzalloc+strcpy+strcat.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>