lantiq: Fix enabling CONFIG_MTD_UIMAGE_SPLIT

r48381 added CONFIG_MTD_SPLIT_UIMAGE_FW=Y to the lantiq kernel
configuration. That unfortunately contains a typo since the "y" has to
be lower-case. This leads to the kernel asking whether the config
symbol should be enabled and thus breaking the build.

FIXES: r48381/feab990887b4: lantiq: Enable the uImage mtd splitter
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

SVN-Revision: 48389