staging: comedi: usbduxsigma: fix unaligned dereferences

There are a couple of dereferences such as `*(uint32_t
*)(devpriv->insn_buf + 1)` that are unaligned as `devpriv->insn_buf` is
of type `uint8_t *`.  This works on x86 architecture but may not be
supported on other architectures.  Call `get_unalign()` to perform the
unaligned dereferences.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Cc: Bernd Porr <mail@berndporr.me.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>