selftests: fix spelling/grammar errors in sysctl/sysctl.sh

Fix the grammatical/spelling errors in sysctl/sysctl.sh.
This fixes all errors pointed out by codespell in the file.

Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>
Signed-off-by: Joel Granados <joel.granados@kernel.org>