rcar_gen3: drivers: pfc: M3N: Drop forward declarations

There's no point in having forward declaration just before the function
itself, drop it. No functional change.
Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Change-Id: I374c4e90729cd13aa4c5878bb3d0917071fa19f1

drivers/staging/renesas/rcar/pfc/M3N/pfc_init_m3n.c

@@ -572,8 +572,6 @@
 #define MOD_SEL2_VIN4_A		((uint32_t)0U << 0U)
 #define MOD_SEL2_VIN4_B		((uint32_t)1U << 0U)
 
-static void pfc_reg_write(uint32_t addr, uint32_t data);
-
 static void pfc_reg_write(uint32_t addr, uint32_t data)
 {
 	mmio_write_32(PFC_PMMR, ~data);