kconfig/nconf: fix compile with ncurses reentrant API

ESCDELAY is a global variable which is replaced by getter and setter
functions with NCURSES_REENTRANT.  This fixes the following error:

nconf.c: In function ‘main’:
nconf.c:1506:2: error: lvalue required as left operand of assignment

Signed-off-by: Yaakov Selkowitz <yselkowitz@users.sourceforge.net>
Signed-off-by: Michal Marek <mmarek@suse.cz>