scripts/spdxcheck: Add percentage to statistics

Files checked:            75856
Lines checked:           294516
Files with SPDX:          59410  78%
Files with errors:            0

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>