haveged: fix CONFIGURE_ARGS

Add backslash to the CONFIGURE_ARGS definition
to remove thread support as originally intended.
The error has been there since the bump to 1.7c.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>
Merge pull request #300 from hnyman/haveged-fix

haveged: fix CONFIGURE_ARGS