staging: vt6656: Refactor the assignment of the phy->signal variable

Create a constant array with the values of the "phy->signal" for every
rate. Remove all "phy->signal" assignments inside the switch statement
and replace these with a single reading from the new vnt_phy_signal
array.

The constant array can be of one dimension because the OR mask with
BIT(3) or BIT(4) allow obtain a second value according to the rate,
the preamble_type and the pkt_type.

Signed-off-by: Oscar Carter <oscar.carter@gmx.com>
Link: https://lore.kernel.org/r/20200414153849.5785-5-oscar.carter@gmx.com


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