net: dpaa2: Use napi_alloc_frag_align() to avoid the memory waste

The napi_alloc_frag_align() will guarantee that a correctly align
buffer address is returned. So use this function to simplify the buffer
alloc and avoid the unnecessary memory waste.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>