fmc: avoid readl/writel namespace conflict

The use of the 'readl' and 'writel' identifiers here causes build errors on
architectures where those are macros. This renames the fields to read32/write32
to avoid the problem.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Alessandro Rubini <rubini@gnudd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>