ghost: Update BB I2C target address
This updates the burnside bridge I2C target addr. to match our expected
configuration.
BRANCH=none
TEST=make passes
#define I2C_ADDR_MP2964_FLAGS 0x20
-#define USBC_PORT_C0_BB_RETIMER_I2C_ADDR 0x57
-#define USBC_PORT_C1_BB_RETIMER_I2C_ADDR 0x57
+#define USBC_PORT_C0_BB_RETIMER_I2C_ADDR 0x56
+#define USBC_PORT_C1_BB_RETIMER_I2C_ADDR 0x56
/* Enabling Thunderbolt-compatible mode */
#define CONFIG_USB_PD_TBT_COMPAT_MODE
