ARM: 8701/1: fix sparse flags for build on 64bit machines

By default sparse uses the characteristics of the build
machine to infer things like the wordsize.
This is fine when doing native builds but for ARM it's,
I suspect, very rarely the case and if the build are done
on a 64bit machine we get a bunch of warnings like:
  'cast truncates bits from constant value (... becomes ...)'

Fix this by adding the -m32 flags for sparse.

Reported-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>