Fix gcc issues in pxa-regs.h

Fix gcc4 issue. With some toolchain, a previous patch that fixes gcc4
issues generates wrong code.
(Problem was reported with gcc-4.0.2-glibc-2.3.6/arm-softfloat-linux-gnu).
This patch fixes the problem and solves the gcc-4 issues as the linux
kernel does.

Signed-off-by: Stefano Babic <sbabic@denx.de>
Signed-off-by: Dmitry Ivanov <ivadmitry@gmail.com>