spi: atmel-quadspi: Fix register name in verbose logging function

`atmel_qspi_reg_name()` is used for pretty-printing register offsets
for verbose logging of register accesses. However, due to a typo
(likely a copy-paste error), QSPI_RD's offset prints as "MR", the
name of the previous register. Fix this typo.

Fixes: c528ecf ("spi: atmel-quadspi: Add verbose debug facilities to monitor register accesses")
Signed-off-by: Csókás, Bence <csokas.bence@prolan.hu>
Reviewed-by: Alexander Dahl <ada@thorsis.com>
Link: https://patch.msgid.link/20241122141302.2599636-1-csokas.bence@prolan.hu
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/atmel-quadspi.c

@@ -183,7 +183,7 @@ static const char *atmel_qspi_reg_name(u32 offset, char *tmp, size_t sz)
 	case QSPI_MR:
 		return "MR";
 	case QSPI_RD:
-		return "MR";
+		return "RD";
 	case QSPI_TD:
 		return "TD";
 	case QSPI_SR: