net: ipa: avoid a bogus warning

The previous commit added support for IPA having up to six source
and destination resources.  But currently nothing uses more than
four.  (Five of each are used in a newer version of the hardware.)

I find that in one of my build environments the compiler complains
about newly-added code in two spots.  Inspection shows that the
warnings have no merit, but this compiler does not recognize that.

    ipa_main.c:457:39: warning: array index 5 is past the end of the
        array (which contains 4 elements) [-Warray-bounds]
    (and the same warning at line 483)

We can make this warning go away by changing the number of elements
in the source and destination resource limit arrays--now rather than
waiting until we need it to support the newer hardware.  This change
was coming soon anyway; make it now to get rid of the warning.

Signed-off-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20201031151524.32132-1-elder@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>