mtd: spi: renesas: Configure DRDRENR register

Make sure DRDRENR register is configured before performing external
address space read. This register might have been configured by a
prior stage bootloader and leaving it unconfigured would interfere
with U-Boot operation. Since U-Boot RPC SPI driver does not support
DDR data transfer mode yet, set this register unconditionally to 0.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
diff --git a/drivers/spi/renesas_rpc_spi.c b/drivers/spi/renesas_rpc_spi.c
index a2ac552..5089098 100644
--- a/drivers/spi/renesas_rpc_spi.c
+++ b/drivers/spi/renesas_rpc_spi.c
@@ -294,6 +294,7 @@
 
 		writel(8 * op->dummy.nbytes - 1, priv->regs + RPC_DRDMCR);
 		writel(0, priv->regs + RPC_DROPR);
+		writel(0, priv->regs + RPC_DRDRENR);
 		writel(smenr, priv->regs + RPC_DRENR);
 
 		memcpy_fromio(din, (void *)(priv->extr + offset), op->data.nbytes);