x86_64 allmodconfig build with W=1 gives these warnings:

drivers/ata/pata_cs5535.c: In function ‘cs5535_set_piomode’:
drivers/ata/pata_cs5535.c:93:11: error: variable ‘dummy’ set but not used [-Werror=unused-but-set-variable]
  u32 reg, dummy;
           ^~~~~
drivers/ata/pata_cs5535.c: In function ‘cs5535_set_dmamode’:
drivers/ata/pata_cs5535.c:132:11: error: variable ‘dummy’ set but not used [-Werror=unused-but-set-variable]
  u32 reg, dummy;
           ^~~~~
cc1: all warnings being treated as errors

Mark variables 'dummy' as "maybe unused" as they are only ever written in
rdmsr() calls.

Signed-off-by: John Garry <redacted>
Reviewed-by: Sergey Shtylyov <redacted>
---
Differences to v1:
- Add RB tag (thanks!)
- Fix commit message

diff --git a/drivers/ata/pata_cs5535.c b/drivers/ata/pata_cs5535.c
index 6725931f3c35..c2c3238ff84b 100644
--- a/drivers/ata/pata_cs5535.c
+++ b/drivers/ata/pata_cs5535.c

@@ -90,7 +90,7 @@ static void cs5535_set_piomode(struct ata_port *ap, struct ata_device *adev)
 	static const u16 pio_cmd_timings[5] = {
 		0xF7F4, 0x53F3, 0x13F1, 0x5131, 0x1131
 	};
-	u32 reg, dummy;
+	u32 reg, __maybe_unused dummy;
 	struct ata_device *pair = ata_dev_pair(adev);
 
 	int mode = adev->pio_mode - XFER_PIO_0;

@@ -129,7 +129,7 @@ static void cs5535_set_dmamode(struct ata_port *ap, struct ata_device *adev)
 	static const u32 mwdma_timings[3] = {
 		0x7F0FFFF3, 0x7F035352, 0x7F024241
 	};
-	u32 reg, dummy;
+	u32 reg, __maybe_unused dummy;
 	int mode = adev->dma_mode;
 
 	rdmsr(ATAC_CH0D0_DMA + 2 * adev->devno, reg, dummy);

-- 
2.35.3