Documentation: kgdb: properly capitalize the MAGIC_SYSRQ config

Most readers are probably going to figure out that the config is actually
all upper-case letters, as all Kconfig symbols are this way.

Properly capitalizing makes the script ./scripts/checkkconfigsymbols.py
happy, which otherwise would report this as a reference to a non-existing
Kconfig symbol.

So, use the right capitalization for the MAGIC_SYSRQ config in the kgdb
documentation.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20211230172423.30430-1-lukas.bulwahn@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/dev-tools/kgdb.rst

@@ -402,7 +402,7 @@ This is a quick example of how to use kdb.
 2. Enter the kernel debugger manually or by waiting for an oops or
    fault. There are several ways you can enter the kernel debugger
    manually; all involve using the :kbd:`SysRq-G`, which means you must have
-   enabled ``CONFIG_MAGIC_SysRq=y`` in your kernel config.
+   enabled ``CONFIG_MAGIC_SYSRQ=y`` in your kernel config.
 
    -  When logged in as root or with a super user session you can run::
 
@@ -461,7 +461,7 @@ This is a quick example of how to use kdb with a keyboard.
 2. Enter the kernel debugger manually or by waiting for an oops or
    fault. There are several ways you can enter the kernel debugger
    manually; all involve using the :kbd:`SysRq-G`, which means you must have
-   enabled ``CONFIG_MAGIC_SysRq=y`` in your kernel config.
+   enabled ``CONFIG_MAGIC_SYSRQ=y`` in your kernel config.
 
    -  When logged in as root or with a super user session you can run::