jme: Fix unmap error (Causing system freeze)

BugLink: http://bugs.launchpad.net/bugs/823296

commit 94c5b41b327e08de0ddf563237855f55080652a1 upstream.

This patch add the missing dma_unmap().
Which solved the critical issue of system freeze on heavy load.

Michal Miroslaw's rejected patch:
[PATCH v2 10/46] net: jme: convert to generic DMA API
Pointed out the issue also, thank you Michal.
But the fix was incorrect. It would unmap needed address
when low memory.

Got lots of feedback from End user and Gentoo Bugzilla.
https://bugs.gentoo.org/show_bug.cgi?id=373109
Thank you all. :)

Signed-off-by: Guo-Fu Tseng <cooldavid@cooldavid.org>
Acked-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>