selftests/powerpc: Fix eeh-basic.sh exit codes

The kselftests test running infrastructure expects tests to finish with an
exit code of 4 if the test decided it should be skipped. Currently
eeh-basic.sh exits with the number of devices that failed to recover, so if
four devices didn't recover we'll report a skip instead of a fail.

Fix this by checking if the return code is non-zero and report success
and failure by returning 0 or 1 respectively. For the cases where should
actually skip return 4.

Fixes: 85d86c8a ("selftests/powerpc: Add basic EEH selftest")
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201014024711.1138386-1-oohall@gmail.com

tools/testing/selftests/powerpc/eeh/eeh-basic.sh

 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0-only
 
+KSELFTESTS_SKIP=4
+
 . ./eeh-functions.sh
 
 if ! eeh_supported ; then
 	echo "EEH not supported on this system, skipping"
-	exit 0;
+	exit $KSELFTESTS_SKIP;
 fi
 
 if [ ! -e "/sys/kernel/debug/powerpc/eeh_dev_check" ] && \
    [ ! -e "/sys/kernel/debug/powerpc/eeh_dev_break" ] ; then
 	echo "debugfs EEH testing files are missing. Is debugfs mounted?"
-	exit 1;
+	exit $KSELFTESTS_SKIP;
 fi
 
 pre_lspci=`mktemp`
@@ -84,4 +86,5 @@ echo "$failed devices failed to recover ($dev_count tested)"
 lspci | diff -u $pre_lspci -
 rm -f $pre_lspci
 
-exit $failed
+test "$failed" == 0
+exit $?