Remove variable declared in prepare from build for AUR helper compatibility

.SRCINFO

@@ -1,7 +1,7 @@
 pkgbase = edgetx-companion
 	pkgdesc = EEPROM Editor and Simulator for EdgeTX RC radio transmitter firmwares
 	pkgver = 2.9.3
-	pkgrel = 1
+	pkgrel = 2
 	url = https://edgetx.org/
 	arch = x86_64
 	license = GPL-2.0-only
@@ -55,6 +55,6 @@ pkgbase = edgetx-companion
 	b2sums = SKIP
 	b2sums = SKIP
 	b2sums = SKIP
-	b2sums = 2f2d110ba03c3d852bec93a0705570df93e72f5e3757bd64494083c5a1ae59c5228024fca563043c05014b1962ccde88e029a6bac2fe36be6e852a53b35a43fb
+	b2sums = 97badff74d64db444a780f48a3003e4a7232e7c0ab1ef43f9adbf20044c988f41dd455dc5aad548e5d3501ccc7a1ad9967a69bf43cbd2bb133eb6d00d50f210c
 
 pkgname = edgetx-companion

PKGBUILD

@@ -5,7 +5,7 @@
 
 pkgname=edgetx-companion
 pkgver=2.9.3
-pkgrel=1
+pkgrel=2
 pkgdesc="EEPROM Editor and Simulator for EdgeTX RC radio transmitter firmwares"
 arch=('x86_64')
 url='https://edgetx.org/'
@@ -70,8 +70,8 @@ prepare() {
 }
 
 build() {
-  cd $_pkgbase
-  ./tools/build-companion.sh $MAKEFLAGS $_pkgbase $srcdir/build
+  cd $srcdir/edgetx
+  ./tools/build-companion.sh $MAKEFLAGS $srcdir/edgetx $srcdir/build
 }
 
 package() {