kernel: add missing symbol for target bcm53xx

Fixes: ca88f4153f8f ("kernel: bump 4.14 to 4.14.77")

Reported-by: Rafał Miłecki <[email protected]>
Signed-off-by: Koen Vandeputte <[email protected]>

target/linux/bcm53xx/config-4.14

@@ -163,6 +163,7 @@ CONFIG_GPIO_74X164=y
 CONFIG_GPIO_SYSFS=y
 # CONFIG_GRO_CELLS is not set
 CONFIG_HANDLE_DOMAIN_IRQ=y
+CONFIG_HARDEN_BRANCH_PREDICTOR=y
 CONFIG_HARDIRQS_SW_RESEND=y
 CONFIG_HAS_DMA=y
 CONFIG_HAS_IOMEM=y