nsdeps: fix hashbang of scripts/nsdeps

This script does not use bash-extension. I am guessing this hashbang
was copied from scripts/coccicheck, which really uses bash-extension.

/bin/sh is enough for this script.

Reviewed-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>