cutelyst: fix kconfig syntax

Commit cb3c56e3 (cutelyst: Add dependency on Kernel headers >= 3.3) used
invalid kconfig syntax, breaking menuconfig:

make menuconfig
package/cutelyst/Config.in:19: syntax error
package/cutelyst/Config.in:18: invalid option
Makefile:900: recipe for target 'menuconfig' failed

Fix it by using 'depends ON' instead.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>