test: Avoid random numbers in dm_test_devm_regmap()

There is no good reason to use a sequence from rand() here. We may as well
invent our own sequence.

This should molify Coverity which does not use rand() being used.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Coverity (CID: 312949)
1 file changed