spi: atmel-quadspi: Fix QSPI_RD reg name on verbose debug

It was wrongly set to "MR", fix it.

Fixes: 52e2565bfb ("spi: atmel-quadspi: Add verbose debug facilities to monitor register accesses")
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
diff --git a/drivers/spi/atmel-quadspi.c b/drivers/spi/atmel-quadspi.c
index b1a3aa9..c8a68e6 100644
--- a/drivers/spi/atmel-quadspi.c
+++ b/drivers/spi/atmel-quadspi.c
@@ -180,7 +180,7 @@
 	case QSPI_MR:
 		return "MR";
 	case QSPI_RD:
-		return "MR";
+		return "RD";
 	case QSPI_TD:
 		return "TD";
 	case QSPI_SR: