misc: genwqe: fix uninitialized return value in genwqe_free_sync_sgl()

Function genwqe_free_sync_sgl() returns the value of variable 'rc'. 'rc' is
only set in the error paths, thus initialize it by 0. Coverity CID 1204242.

Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>