Changed PreferenceCategory left padding.

For a reason I didn't have time to investigate further, the
old 5sp value was not used in a standard PreferenceCategory,
the left and right padding being set to 8dip for these.

For other users of this style, this change sets the right
padding value of 8dip.

Change-Id: Ia8a7b6ffc9e1dc99b98415dcc141eb7277f6da28