docbook: change iomap source filename in deviceiobook

Fix warning since kernel-doc comments were moved to another
source file.

Warning(lib/iomap.c): no structured comments found
Signed-off-by: NRandy Dunlap <rdunlap@xenotime.net>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/DocBook/deviceiobook.tmpl

@@ -317,7 +317,7 @@ CPU B:  spin_unlock_irqrestore(&dev_lock, flags)
   <chapter id="pubfunctions">
      <title>Public Functions Provided</title>
 !Iarch/x86/include/asm/io.h
-!Elib/iomap.c
+!Elib/pci_iomap.c
   </chapter>
 
 </book>