Move patching to prepare()

.SRCINFO

@@ -1,5 +1,5 @@
 # Generated by mksrcinfo v8
-# Tue Jan 31 20:09:33 UTC 2017
+# Tue Jan 31 20:55:25 UTC 2017
 pkgbase = bbswitch-dkms-git
 	pkgdesc = kernel module allowing to switch dedicated graphics card on Optimus laptops, dkms version
 	pkgver = 0.8.r0.g0c38f97

PKGBUILD

@@ -26,11 +26,15 @@ pkgver() {
     git describe --long | sed -r 's/^v//;s/([^-]*-g)/r\1/;s/-/./g'
 }
 
-package() {
+prepare() {
   cd "${srcdir}/${_pkgname}"
 
   # Exceprt adapted from upstream Makefile.dkms
   sed -e "s/#MODULE_VERSION#/${pkgver}/" -i "dkms/dkms.conf"
+}
+
+package() {
+  cd "${srcdir}/${_pkgname}"
 
   install -dm755 "${pkgdir}/usr/src/${_pkgname}-${pkgver}"
   install -Dm644 Makefile bbswitch.c dkms/dkms.conf "${pkgdir}/usr/src/${_pkgname}-${pkgver}"