Fix registering shortcut for text editor actions

Broke with f1eb9c4827670a56a5f772575d7f4a1d1f9cd26f which exchanged
setDefaultKeySequence with setKeySequence

Task-number: QTCREATORBUG-10538
Change-Id: Id40bd8fd403cd586a39a19c248f59e23cf4cf8c0
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: David Schulz <david.schulz@digia.com>