less: depends on curses

The less package already selects BR2_PACKAGE_CURSES, but it fails to
depend on it in the makefile. Therefore, there are cases where less
gets built before curses, and the build fails:

checking for working terminal libraries... Cannot find terminal libraries - configure failed

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>