ide-cd: add missing 'ireason' masking to cdrom_write_intr()

Mask 'ireason' variable with 0x3 so the valid interrupt reason value
is passed to cdrom_write_check_ireason() for checking.
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/ide-cd.c

@@ -1826,7 +1826,7 @@ static ide_startstop_t cdrom_write_intr(ide_drive_t *drive)
 	}
 
 	/* Read the interrupt reason and the transfer length. */
-	ireason = HWIF(drive)->INB(IDE_IREASON_REG);
+	ireason = HWIF(drive)->INB(IDE_IREASON_REG) & 0x3;
 	lowcyl  = HWIF(drive)->INB(IDE_BCOUNTL_REG);
 	highcyl = HWIF(drive)->INB(IDE_BCOUNTH_REG);