package/qt5serialport: update hash source URL

Be more specific for the hash source URL and change from
summary page (.mirrorlist) to direct sha256 download page
(.sha256).

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/qt5/qt5serialport/5.12.7/qt5serialport.hash

@@ -1,4 +1,4 @@
-# Hash from: https://download.qt.io/official_releases/qt/5.12/5.12.7/submodules/qtserialport-everywhere-src-5.12.7.tar.xz.mirrorlist
+# Hash from: https://download.qt.io/official_releases/qt/5.12/5.12.7/submodules/qtserialport-everywhere-src-5.12.7.tar.xz.sha256
 sha256 224c282ebed750f46b72dfe18260c3d26fbb74e928dec64bd8c51e7beed8721f qtserialport-everywhere-src-5.12.7.tar.xz
 
 # Hashes for license files: