x86: init_mem_mapping(): use capital BIOS in comment

Use capital BIOS in comment. Its cleaner, and allows diference
between BIOS and BIOs.
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

arch/x86/mm/init.c

@@ -582,7 +582,7 @@ void __init init_mem_mapping(void)
  *
  *
  * On x86, access has to be given to the first megabyte of ram because that area
- * contains bios code and data regions used by X and dosemu and similar apps.
+ * contains BIOS code and data regions used by X and dosemu and similar apps.
  * Access has to be given to non-kernel-ram areas as well, these contain the PCI
  * mmio resources as well as potential bios/acpi data regions.
  */