generatelocales: fix 'cut' invocation

'cut' needs to be invoked with the -s option to make sure it doesn't
print anything when the delimiter isn't found. This is particularly
important for the charmap detection, because UTF-8 is appended if
the charmap is empty. But without -s, it will never be empty.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>