ref-manual: variables: fix spurious parenthesis

There's no opening parenthesis, so let's remove the spurious closing
parenthesis.

Fixes: ea638e85316d ("ref-manual/variables: document the KERNEL_CONSOLE variable")
(From yocto-docs rev: 6f0e150179db2a2a8e9ad879167e0d84137190dc)

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/variables.rst

@@ -4631,7 +4631,7 @@ system and gives an overview of their function and contents.
 
      The default value of this variable is extracted from the first console
      device and setting in :term:`SERIAL_CONSOLES`. If nothing is found in
-     :term:`SERIAL_CONSOLES`, the default value is set to ``ttyS0,115200``).
+     :term:`SERIAL_CONSOLES`, the default value is set to ``ttyS0,115200``.
 
      For more information, see the `Kernel command-line documentation
      <https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html>`__.