Revert "linux: fix check of configuration file existence"

This reverts commit 477c28cf1d637b224b819dd278103a05fb6f9dbb. The
whole host-lzop optional dependency logic cannot work, since the
configuration file will only be known after the kernel sources are
extracted, if an internal kernel defconfig is used, which is quite
common.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

linux/linux.mk

@@ -166,11 +166,9 @@ else ifeq ($(BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG),y)
 KERNEL_SOURCE_CONFIG = $(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE))
 endif
 
-ifeq ($(BR2_LINUX_KERNEL),y)
 ifeq ($(wildcard $(KERNEL_SOURCE_CONFIG)),)
 $(error Configuration file '$(KERNEL_SOURCE_CONFIG)' not found.)
 endif
-endif
 
 ifeq ($(call KCONFIG_GET_OPT,CONFIG_KERNEL_LZO,$(KERNEL_SOURCE_CONFIG)),y)
 LINUX_DEPENDENCIES += host-lzop