staging: comedi: amplc_pc236: don't check bus type in attach

Since the legacy attach routine `pc236_attach()` is only called for
board names matching an entry in our array of ISA boards
`pc236_isa_boards[]`, and it is reasonable to expect all elements of
`pc236_isa_boards[]` to have their `bustype` member initialized
correctly to `isa_bustype`, don't bother checking the bus type in
`pc236_attach()`.  Add `if (!DO_ISA) return -EINVAL` to optimize out the
remainder of the function if `CONFIG_COMEDI_AMPLC_PC236_ISA` is not
defined.

Similarly, don't bother checking the bus type in
`pc236_find_pci_board()` as it is reasonable to expect all elements of
`pc236_pci_boards[]` to have their `bustype` member initialized
correctly to `pci_bustype`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>