MT#56627 el/rtpengine.spec: fix version handling for dkms
In commit 427615d45b we switched to usage of dh-sequence-dkms. By
renaming debian/dkms.conf.in into debian/ngcp-rtpengine-kernel-dkms.dkms
and replacing its `__VERSION__` with `#MODULE_VERSION#` we broke the
shipped RPM spec file, which also relies on our dkms configuration file.
Accordingly adapt el/rtpengine.spec.
Thanks to @themsley-voiceflex for the bug report
Closes#1650
Change-Id: I257a8c223f931bb959f245ed518b855ffa988a81