PNP: system.c: unmark a comment as being kernel-doc

Fix a documentation build warning caused by the comment not being
in kernel-doc format:

system.c:110: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
* Reserve motherboard resources after PCI claim BARs,

Signed-off-by: Randy Dunlap <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/pnp/system.c

···
 	return pnp_register_driver(&system_pnp_driver);
 }
 
-/**
+/*
  * Reserve motherboard resources after PCI claim BARs,
  * but before PCI assign resources for uninitialized PCI devices
  */