staging: vt6656: Use defines in preamble_type variables

Use the PREAMBLE_SHORT and PREAMBLE_LONG defines present in the file
"baseband.h" to assign values to preamble_type variables. Also, use the
same defines to make comparisons against these variables.

In this way, avoid the use of numerical literals or boolean values and
make the code more clear.

Signed-off-by: Oscar Carter <oscar.carter@gmx.com>
Reviewed-by: Quentin Deslandes <quentin.deslandes@itdev.co.uk>
Link: https://lore.kernel.org/r/20200328141738.23810-1-oscar.carter@gmx.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>