Brendan Donovan’s absence has made it pretty clear that the Mariners’ lineup is better when his skill set is in it. His expected return from the injured list will not solve every offensive concern, but it should give Seattle back one of its most important connective pieces. According to Daniel Kramer of MLB.com, Donovan is tentatively targeted to return from the injured list at some point during the Mariners’ upcoming six-game homestand against the Kansas City Royals and Atlanta Braves, which begins Friday. Donovan has remained in Seattle during the club’s road trip while continuing baseball activity at T-Mobile Park, and Dan Wilson said the progression has “gone as hoped.”   Donovan landed on the injured list with a left groin muscle strain, an issue connected to a larger physical picture after Donovan underwent sports hernia surgery last October while still with the Cardinals.…