samples/bpf: Fix typos in README

This change fixes some typos found in the BPF samples README file.

Signed-off-by: Daniel Müller <deso@posteo.net>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20221018163231.1926462-1-deso@posteo.net


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>