bpf: Fix spelling in bpf_verifier.h

Minor spelling fix spotted in bpf_verifier.h. Spelling is no big deal,
but it is still an improvement when reading through the code.

Signed-off-by: Hongyi Lu <jwnhy0@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220613211633.58647-1-jwnhy0@gmail.com