[COMMON] android: ion: fix overwriting gfp flags

[COMMON] android: ion: fix overwriting gfp flags

The following commit by Chen Feng introduces cached page pools to
improve the allocation perfromance of system heap types.
'commit e7f63771b60e ("ION: Sys_heap: Add cached pool to spead up
 cached buffer alloc")'

But it has a logical problem assigning gfp mask for page allocation
from the kernel page allocator. low_order_gfp_flags should be applied
to the low order page allocations but is is actually not because
high_order_gfp_flags overwrites the gfp_flags at the first iteration
of page pool creation and there is no chance to get back to
low_order_gfp_flags.

Change-Id: I4fb10bfc9f517e660e2f78661d67146380441ecb
Signed-off-by: Cho KyongHo <pullip.cho@samsung.com>