Update LightSettingsDialog.java

Colour picker text input field: wrong content due to alpha channel.

The field was, effectively, showing AARRGG instead of RRGGBB due to
the alpha component being non-zero. This change fixes that in a
generic way which allows for alpha channel handling even though I see
no use for the alpha channel for the notification light.
Change-Id: I5b71340f3b644c6f6b305dc66d1285cc77427bf5