Revert "fs/nls: make load_nls() take a const parameter"

This reverts commit 5b64fc24 which is
commit c1ed39ec upstream.

It changes the signature of a ABI-frozen function, while nice to have,
isn't actually needed right now, so revert it to preserve the Android
abi.

Bug: 161946584
Change-Id: I49f5124db00ac2aedd5d96c3aedde80c4ad11664
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>