staging: comedi: jr3_pci: pass transform by reference

Local function `set_transforms` has a parameter of type `struct
jr3_pci_transform`.  This has a size 32 bytes, which is quite large for
passing around in a function call.  Change it to use type `const struct
jr3_pci_transform *`.  (In practice, it is probably inlined by the
compiler anyway, but doing this seems to save a few bytes.)

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>