rslib: Simplify error path

The four error path labels in rs_init() can be reduced to one by allocating
the struct with kzalloc so the pointers in the struct are NULL and can be
unconditionally handed in to kfree() because they either point to an
allocation or are NULL.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kees Cook <keescook@chromium.org>