net: ipa: don't assume mem array indexed by ID

Change ipa_mem_valid() to iterate over the entries using a u32 index
variable rather than using a memory region ID.  Use the ID found
inside the memory descriptor rather than the loop index.

Change ipa_mem_size_valid() to iterate over the entries but without
assuming the array index is the memory region ID.  "Empty" entries
will have zero size; and we'll temporarily assume such entries have
zero offset as well (they all do, currently).

Similarly, don't assume the mem[] array is indexed by ID in
ipa_mem_config().  There, "empty" entries will have a zero canary
count, so no special assumptions are needed to handle them correctly.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>