tools/power turbostat: fix leak of file descriptor on error return path

Currently the error return path does not close the file fp and leaks
a file descriptor. Fix this by closing the file.

Fixes: 5ea7647b

 ("tools/power turbostat: Warn on bad ACPI LPIT data")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Len Brown <len.brown@intel.com>