staging: comedi: das1800: change type of private data 'fifo_buf'

Fix the checkpatch.pl issue:
CHECK: Prefer kernel type 'u16' over 'uint16_t'

Change the type to 'unsigned short' as that is more typical in comedi
drivers.

Use sizeof(*p) instead of sizeof(type) when allocation the buffer.
Also fix the checkpatch.pl issue:
WARNING: line over 80 characters

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