dt-bindings: phy: Update SERDES_MAX to be SERDES_MAX + 1

SERDES_MAX is a valid value to index ctrl->phys in
drivers/phy/mscc/phy-ocelot-serdes.c. But, currently,
there is an out-of-bounds bug in the mentioned driver
when reading from ctrl->phys, because the size of
array ctrl->phys is SERDES_MAX.

Partially fix this by updating SERDES_MAX to be SERDES6G_MAX + 1.

Notice that this is the first part of the solution to
the out-of-bounds bug mentioned above. Although this
change is not dependent on any other one.

Suggested-by: Quentin Schulz <[e-mail]>
Reviewed-by: Quentin Schulz <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/dt-bindings/phy/phy-ocelot-serdes.h

···
 #define SERDES1G_MAX	SERDES1G(5)
 #define SERDES6G(x)	(SERDES1G_MAX + 1 + (x))
 #define SERDES6G_MAX	SERDES6G(2)
-#define SERDES_MAX	SERDES6G_MAX
+#define SERDES_MAX	(SERDES6G_MAX + 1)
 
 #endif