Documentation: remove invalid fragment type specifier

Change-Id: I1a07180532c6fa7c7ac487e39632438eef3b34e7
Signed-off-by: Patrick Georgi <patrick@georgi.software>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35815
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

Documentation/superio/common/ssdt.md

@@ -19,7 +19,7 @@ I/O range and ISA IRQ number.
 
 This example is based on AST2400.
 
-```code
+```
 # Add a "container" for proper ACPI code generation
 chip superio/common
   device pnp 2e.0 on # just for the base device, not for the LDNs