rcar_gen3: plat: Add missing dependency to rcar_srecord

Add missing dependency on the bl2.elf and bl31.elf into the rcar_srecord
target, which uses those ELF files to generate the SRECs.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>

plat/renesas/rcar/platform.mk

@@ -415,7 +415,7 @@ clean_srecord:
 	rm -f ${SREC_PATH}/bl2.srec ${SREC_PATH}/bl31.srec
 
 .PHONY: rcar_srecord
-rcar_srecord:
+rcar_srecord: $(BL2_ELF_SRC) $(BL31_ELF_SRC)
 	@echo "generating srec: ${SREC_PATH}/bl2.srec"
 	$(Q)$(OC) -O srec --srec-forceS3 ${BL2_ELF_SRC}  ${SREC_PATH}/bl2.srec
 	@echo "generating srec: ${SREC_PATH}/bl31.srec"