dlm: match signedness between dlm_config_info and cluster_set

cluster_set is only called from the macro CLUSTER_ATTR which defines read/write
access functions.  Make the signedness match to avoid sparse warnings every time
CLUSTER_ATTR is used (lines 149-159) all of the form:

fs/dlm/config.c:149:1: warning: incorrect type in argument 3 (different signedness)
fs/dlm/config.c:149:1:    expected unsigned int *info_field
fs/dlm/config.c:149:1:    got int extern [toplevel] *<noident>

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: David Teigland <teigland@redhat.com>