net: vertexcom: mse102x: Fix LEN_MASK

The LEN_MASK for CMD_RTS doesn't cover the whole parameter mask.
The Bit 11 is reserved, so adjust LEN_MASK accordingly.

Fixes: 2f207cb ("net: vertexcom: Add MSE102x SPI support")
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250430133043.7722-3-wahrenst@gmx.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: lategoodbye

drivers/net/ethernet/vertexcom/mse102x.c

@@ -33,7 +33,7 @@
 #define CMD_CTR		(0x2 << CMD_SHIFT)
 
 #define CMD_MASK	GENMASK(15, CMD_SHIFT)
-#define LEN_MASK	GENMASK(CMD_SHIFT - 1, 0)
+#define LEN_MASK	GENMASK(CMD_SHIFT - 2, 0)
 
 #define DET_CMD_LEN	4
 #define DET_SOF_LEN	2