Add missing iounmap in error handling code, in a case where the function
already preforms iounmap on some other execution path.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression e;
statement S,S1;
int ret;
@@
e = \(ioremap\|ioremap_nocache\)(...)
... when != iounmap(e)
if (<+...e...+>) S
... when any
    when != iounmap(e)
*if (...)
   { ... when != iounmap(e)
     return ...; }
... when any
iounmap(e);
// </smpl>
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
[fixed up subject -jstultz]
Signed-off-by: John Stultz <john.stultz@linaro.org>