If any filename in the intramfs dependency
list contains a colon, that causes a kernel
build error like this:

/devel/openwrt/build_dir/linux-ar71xx_generic/linux-3.6.6/usr/Makefile:58: *** multiple target patterns.  Stop.
make[5]: *** [usr] Error 2

Fix it by removing such filenames from the
deps_initramfs list.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>