Documentation: samsung-s3c24xx: Add blank line after SPDX directive

After merging spdx tree for linux-next testing, Stephen Rothwell reported
htmldocs warning:

Documentation/arm/samsung-s3c24xx/cpufreq.rst:2: WARNING: Explicit markup ends without a blank line; unexpected unindent.

It is due to missing blank line separator between SPDX directive and
page title.

Add the blank line to fix the warning.

Link: https://lore.kernel.org/linux-next/20220614164506.6afd65a6@canb.auug.org.au/
Fixes: b7bc1c9e ("treewide: Replace GPLv2 boilerplate/reference with SPDX - gpl-2.0_147.RULE")
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Allison Randal <allison@lohutok.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/arm/samsung-s3c24xx/cpufreq.rst

 .. SPDX-License-Identifier: GPL-2.0-only
+
 =======================
 S3C24XX CPUfreq support
 =======================