main/libdrm-grate: fix pkgver (!565)

The libdrm version is 2.4.96 according to configure.ac

temp/libdrm-grate/APKBUILD

 # Forked from Alpine, so we can build it with Grate support
 pkgname=libdrm-grate
-pkgver=2.4.91
-pkgrel=2
+pkgver=2.4.96_git20190318
+pkgrel=0
 pkgdesc="Userspace interface to kernel DRM services"
 url="https://github.com/grate-driver/libdrm"
 arch="armhf armv7"