x86: fix mtrr missing kernel-doc

Fix missing kernel-doc notation in mtrr/main.c:

Warning(arch/x86/kernel/cpu/mtrr/main.c:152): No description found for parameter 'info'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>