agp/uninorth: fix a memleak in create_gatt_table

Fix the memory leak in create_gatt_table:
we've lost a kfree on the exit path for the pages array allocated
in uninorth_create_gatt_table

Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>