stm32mp1: remove duplicate function declaration

It is already in include/drivers/st/stm32mp1_ddr_helpers.h.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/include/drivers/st/stm32mp1_ddr_regs.h b/include/drivers/st/stm32mp1_ddr_regs.h
index 9598d9b..288e072 100644
--- a/include/drivers/st/stm32mp1_ddr_regs.h
+++ b/include/drivers/st/stm32mp1_ddr_regs.h
@@ -408,6 +408,4 @@
 #define DDRPHYC_DXNDLLCR_SDPHASE_MASK		GENMASK(17, 14)
 #define DDRPHYC_DXNDLLCR_SDPHASE_SHIFT		14
 
-void ddr_enable_clock(void);
-
 #endif /* STM32MP1_DDR_REGS_H */