bpftool: Fix typos

Fix typos in documentation.

Reported-by: Matthew Wilcox <willy@infradead.org>
Reported-by: Quentin Monnet <qmo@kernel.org>
Signed-off-by: Andrew Kreimer <algonell@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Quentin Monnet <qmo@kernel.org>
Link: https://lore.kernel.org/bpf/20240909092452.4293-1-algonell@gmail.com