staging: pi433: remove hardcoded mask value for easier readability

replace hardcoded value with the bitwise complement of the mask used to
extract value sent to rf69 chip.
Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Link: https://lore.kernel.org/r/YicPRrH3HmpiTCxe@mail.google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/pi433/rf69.c

@@ -741,7 +741,7 @@ int rf69_set_fifo_threshold(struct spi_device *spi, u8 threshold)
 	int retval;
 
 	/* check input value */
-	if (threshold & 0x80) {
+	if (threshold & ~MASK_FIFO_THRESH_VALUE) {
 		dev_dbg(&spi->dev, "set: illegal fifo threshold %u\n", threshold);
 		return -EINVAL;
 	}