x86: fix readb() et al compile error with gcc-3.2.3

Building 2.6.27-rc1 on x86 with gcc-3.2.3 fails with:

In file included from include/asm/dma.h:12,
                 from include/linux/bootmem.h:8,
                 from init/main.c:26:
include/asm/io.h: In function `readb':
include/asm/io.h:32: syntax error before string constant
include/asm/io.h: In function `readw':
include/asm/io.h:33: syntax error before string constant
include/asm/io.h: In function `readl':
include/asm/io.h:34: syntax error before string constant
include/asm/io.h: In function `__readb':
include/asm/io.h:36: syntax error before string constant
include/asm/io.h: In function `__readw':
include/asm/io.h:37: syntax error before string constant
include/asm/io.h: In function `__readl':
include/asm/io.h:38: syntax error before string constant
make[1]: *** [init/main.o] Error 1
make: *** [init] Error 2

Starting with 2.6.27-rc1 readb() et al are generated by a
build_mmio_read() macro, which generates asm() statements with
output register constraints like "=" "q", i.e. as two adjacent
string literals. This doesn't work with gcc-3.2.3.

Fixed by moving the "=" part into the callers' reg parameter
(as suggested by Ingo).

Build and boot-tested with gcc-3.2.3 on 32 and 64-bit x86.

Fixes <http://bugzilla.kernel.org/show_bug.cgi?id=11205>.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Ingo Molnar <mingo@elte.hu>