bpf: Fix a few typos in BPF helpers documentation

bpf: Fix a few typos in BPF helpers documentation

Address a few typos in the documentation for the BPF helper functions.
They were reported by Jakub [0], who ran spell checkers on the generated
man page [1].

[0] https://lore.kernel.org/linux-man/d22dcd47-023c-8f52-d369-7b5308e6c842@gmail.com/T/#mb02e7d4b7fb61d98fa914c77b581184e9a9537af
[1] https://lore.kernel.org/linux-man/eb6a1e41-c48e-ac45-5154-ac57a2c76108@gmail.com/T/#m4a8d1b003616928013ffcd1450437309ab652f9f

v3: Do not copy unrelated (and breaking) elements to tools/ header
v2: Turn a ',' into a ';'

Reported-by: Jakub Wilk <jwilk@jwilk.net>
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220825220806.107143-1-quentin@isovalent.com