This is a VCS package which should have the -git suffix. I’ve submitted a deletion request. Please resubmit it as rtl8188gu-dkms-git.
To address your concern:
Your pkgver function is malformed. There are no tags, so the v1.0 you’re shoving in there improperly is why there’s an invalid reference. Do not invent a pkgver, always generate it from the upstream repo. See VCS package guidelines - ArchWiki
Do not use unneeded variables like $_pkgbase. For one, it’s the same as your pkgname so it’s redundant and pointless. There’s already a pkgbase which is not needed here.
Do not skip checksums for files
Use install -d instead of mkdir
Use install -DmXXX to install files with the proper permissions
EDIT: rtl8188gu-dkms is now deleted and I see you resubmitted it as rtl8188gu-dkms-git. That’s great, however you haven’t changed the pkgver function which was the topic of this thread.
I thought you were including a custom one for a reason. I edited my post again. No reason to explicitly install the upstream dkms.conf then because it gets copied along with everything else. Post above edited to reflect that.