selftests: static_keys: fix test name in messages

As a general rule, the name of the selftest is printed at the beginning
of every message.

Use "static_keys" (name of the test itself) consistently instead of mixing
"static_key" and "static_keys" at the beginning of the messages in the
test_static_keys script.

Signed-off-by: Javier Carrasco <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/static_keys/test_static_keys.sh

···
 ksft_skip=4
 
 if ! /sbin/modprobe -q -n test_static_key_base; then
-	echo "static_key: module test_static_key_base is not found [SKIP]"
+	echo "static_keys: module test_static_key_base is not found [SKIP]"
 	exit $ksft_skip
 fi
 
 if ! /sbin/modprobe -q -n test_static_keys; then
-	echo "static_key: module test_static_keys is not found [SKIP]"
+	echo "static_keys: module test_static_keys is not found [SKIP]"
 	exit $ksft_skip
 fi
 
 if /sbin/modprobe -q test_static_key_base; then
 	if /sbin/modprobe -q test_static_keys; then
-		echo "static_key: ok"
+		echo "static_keys: ok"
 		/sbin/modprobe -q -r test_static_keys
 		/sbin/modprobe -q -r test_static_key_base
 	else
···
 		/sbin/modprobe -q -r test_static_key_base
 	fi
 else
-	echo "static_key: [FAIL]"
+	echo "static_keys: [FAIL]"
 	exit 1
 fi