nano: fix ncursesw build failure

nano: fix ncursesw build failure

After the latest version bump ncursesw5-config is automatically detected
if it's present in the build machine (almost always because we need full
ncurses support with headers for Kconfig's menuconfig).
Since we don't have ncursesw support in buildroot just say no. Fixes:
http://autobuild.buildroot.net/results/89d/89d7ec7306411b15f9ffbc2051d0d316237b4c07/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>