device tree will be used to determine what chip selects are valid.
Return -ENODEV if the supplied chip select is invalid, or 0 if it is valid.
-If you don't provide the cs_info() method, -ENODEV is assumed for all
-chip selects that do not appear in the device tree.
+If you don't provide the cs_info() method, 0 is assumed for all chip selects
+that do not appear in the device tree.
Test it