Calling vector_state_store_savectx() overwrites ra with the address of
the following ret instruction. The ret consequently branches to itself
and prevents kernel dumps from progressing past dump_savectx().
Tail-call vector_state_store_savectx() so that it returns directly to
the original savectx() caller.
Fixes: d7a393095cfd ("riscv: Vector Extension (RVV) support.")
Sponsored by: FreeBSD Foundation