request_mem_region returns NULL when requesting the region failed, and
a valid pointer when it was successful. Currently the condition is
inverted.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46452 3c298f89-4303-0410-b956-a3cf2f4a3e73