brcmfmac: work-around gcc 4.7 build issue

Alexandre Oliva <oliva@lsd.ic.unicamp.br> says:

"It's an issue brought about by GCC 4.7's partial-inlining, that ends up
splitting the udelay function just at the wrong spot, in such a way that
some sanity checks for constants fails, and we end up calling
bad_udelay.

This patch fixes the problem.  Feel free to push it upstream if it makes
sense to you."

Signed-off-by: John W. Linville <linville@tuxdriver.com>