device-raspberry-pi4: depend on linux-rpi instead of linux-rpi4 (MR 4903)

Name of package in aports is linux-rpi these days. linux-rpi provides
linux-rpi4 for backward compatibility, so depending on linux-rpi4
still works, but lets use real package name so that it is easier to
find.

device/testing/device-raspberry-pi4/APKBUILD

@@ -8,7 +8,7 @@ url="https://postmarketos.org"
 license="MIT"
 arch="aarch64"
 options="!check !archcheck"
-depends="postmarketos-base raspberrypi-bootloader linux-rpi4"
+depends="postmarketos-base raspberrypi-bootloader linux-rpi"
 makedepends="devicepkg-dev"
 install="$pkgname.post-install $pkgname.post-upgrade"
 subpackages="