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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/pi433/rf69.c

···
 	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;
 	}