error_reporting: Fix return value description

[imme-emosol]

No description provided.

[TimWolla]

Thank you!

[imme-emosol]

I just realized that a strict interpretation of the wording might read to mean:

• first return the value,
• then change it.

Which is probably not how it works.

As such, a nitpick suggestion:

- Returns the error_reporting level, before it is changed to error_level.
+ Returns the error_reporting level, as before it was changed to error_level.