spi: dw: Use regset32 DebugFS method to create regdump file

DebugFS kernel interface provides a dedicated method to create the
registers dump file. Use it instead of creating a generic DebugFS
file with manually written read callback function.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>
Cc: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org
Link: https://lore.kernel.org/r/20200529131205.31838-16-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
index 0b2cd79..151ba316 100644
--- a/drivers/spi/spi-dw.h
+++ b/drivers/spi/spi-dw.h
@@ -3,6 +3,7 @@
 #define DW_SPI_HEADER_H
 
 #include <linux/completion.h>
+#include <linux/debugfs.h>
 #include <linux/irqreturn.h>
 #include <linux/io.h>
 #include <linux/scatterlist.h>
@@ -152,6 +153,7 @@ struct dw_spi {
 
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *debugfs;
+	struct debugfs_regset32 regset;
 #endif
 };