Bug 8834 - Call to C4::Context::preference fails to pass $self in Circulation.pm

Bug 8834 - Call to C4::Context::preference fails to pass $self in Circulation.pm

Changed:
    my $circcontrol = C4::Context::preference('CircControl');
To:
    my $circcontrol = C4::Context->preference('CircControl');
This will pass $self and 'CircControl' which will then prevent
a "Use of uninitialized value" error log entry.

Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>