[BUGFIX] Fix call to strpos to find port number

With the introduction of lazy database loading we introduced
a bug for database host strings with a port number. This patch
fixes the call to strpos() by switching the arguments.

Fixes: #47221
Releases: 6.1
Related: #46880
Change-Id: I1da875b7be531929f96f3496e6a1357638a80305
Reviewed-on: https://review.typo3.org/19978
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Felix Kopp
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn