revokefs: Use the right variable name in an error message
revokefs: Use the right variable name in an error message

scan-build detected that response_size is uninitialized here, presumably
a typo for response_data_size.

Signed-off-by: Simon McVittie <0e1aea601907c1a85c2dc96e5ea37e23c58d2e9b@collabora.com>

flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak