staging: comedi: amplc_pci230: collapse some 'else { if' chains

Where the only thing in an `else { ... }` block is another `if`
statement, collapse it to an `else if {` block where it makes sense to
do so.

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>