Documentation: fix ioremap return type

ioremap() returns a void __iomem * not a char *.  Update the documentation
file to reflect this.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/IO-mapping.txt

@@ -157,7 +157,7 @@ For such memory, you can do things like
 	 * access only the 640k-1MB area, so anything else
 	 * has to be remapped.
 	 */
-	char * baseptr = ioremap(0xFC000000, 1024*1024);
+	void __iomem *baseptr = ioremap(0xFC000000, 1024*1024);
 
 	/* write a 'A' to the offset 10 of the area */
 	writeb('A',baseptr+10);