package/qt5base: fix qmake parallel build

package/qt5base: fix qmake parallel build

When configuring qt5base, qmake is built, but it's not built in parallel
mode. This is due to MAKEFLAGS having 2 dashes on its tail, so this:
MAKEFLAGS="$(MAKEFLAGS) -j$(PARALLEL_JOBS)"
expands in this(i.e. 5 njobs):
MAKEFLAGS="--no-print-directory -- -j5"
and -j5 gets ignored due to "--" preceeding -j5.
Double dashes are part of $(MAKEFLAGS) only when evaluated by shell.

Swap $(MAKEFLAGS) and -j$(PARALLEL_JOBS) to avoid having "--" before
-j$(PARALLEL_JOBS), this way -j$(PARALLEL_JOBS) won't be ignored by
./configure.

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Tested-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>