lib/repo-commit: Fix min-free-space error message
lib/repo-commit: Fix min-free-space error message

Since min_free_space_size_mb is considered before min_free_space_percent
in min_free_space_calculate_reserved_blocks(), it has to be considered
first when generating the error message in order for it to be accurate.

Closes: #1691
Approved by: jlebon

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree