kernel: Move to Linux v4.15.14-openpower1

Adds a fix for a race when EEH devices are unbound, which was seen with
the NVMe driver.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/openpower/configs/romulus_defconfig b/openpower/configs/romulus_defconfig
index 6759b1c..301e824 100644
--- a/openpower/configs/romulus_defconfig
+++ b/openpower/configs/romulus_defconfig
@@ -14,7 +14,7 @@
 BR2_ROOTFS_POST_BUILD_SCRIPT="../openpower/scripts/fixup-target-var ../openpower/scripts/firmware-whitelist"
 BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_CUSTOM_VERSION=y
-BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.15.9"
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.15.14"
 BR2_LINUX_KERNEL_PATCH="$(BR2_EXTERNAL_OP_BUILD_PATH)/linux"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
 BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(BR2_EXTERNAL_OP_BUILD_PATH)/configs/linux/skiroot_p9_defconfig"