tests: shell: fix spurious dump failure in vmap timeout test

tests: shell: fix spurious dump failure in vmap timeout test

Blamed commit can update the timeout to 6s, but last line waits
for 5 seconds and expects that to be enough to have all elements vanish.

Fix the typo to limit update timeout also to 5 seconds and not 6.
This fixes spurious dump failures like this one:

-               elements = { 1.2.3.4 . 22 : jump ssh_input }
+               elements = { 1.2.3.4 . 22 : jump ssh_input,
+                            10.0.95.144 . 38023 timeout 6s expires 545ms : jump other_input }

Fixes: db80037c0279 ("tests: shell: extend vmap test with updates")
Signed-off-by: Florian Westphal <fw@strlen.de>