kernel: add missing symbol

Signed-off-by: John Crispin <[email protected]>

target/linux/generic/config-4.14

@@ -1270,6 +1270,7 @@ CONFIG_EXPERT=y
 CONFIG_EXT4_USE_FOR_EXT2=y
 # CONFIG_EXTCON is not set
 # CONFIG_EXTCON_ADC_JACK is not set
+# CONFIG_EXTCON_AXP288 is not set
 # CONFIG_EXTCON_GPIO is not set
 # CONFIG_EXTCON_INTEL_INT3496 is not set
 # CONFIG_EXTCON_MAX3355 is not set

target/linux/generic/config-4.9

@@ -1194,6 +1194,7 @@ CONFIG_EXPERT=y
 CONFIG_EXT4_USE_FOR_EXT2=y
 # CONFIG_EXTCON is not set
 # CONFIG_EXTCON_ADC_JACK is not set
+# CONFIG_EXTCON_AXP288 is not set
 # CONFIG_EXTCON_GPIO is not set
 # CONFIG_EXTCON_MAX3355 is not set
 # CONFIG_EXTCON_QCOM_SPMI_MISC is not set