IDE: Save a call to PageHighMem()

PageHighMem() isn't cheap so avoid calling it twice on the same page.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>