staging: comedi: acl7225b: cleanup acl7225b_do_insn_bits()

Use a local variable to hold the base register, 'reg', that is used
to write to the relays.

Add local variables for the 'mask' and 'bits' values used to update
the relays.

The relays only need to be updated if the 'mask' is set. Move the outb()
calls into the if (mask) to make this clearer.

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