MIPS: VDSO: avoid duplicate CAC_BASE definition

vdso.h includes <spaces.h> implicitly after defining CONFIG_32BITS.
This defeats the override in mach-ip27/spaces.h, leading to
a build error that shows up in kernelci.org:

In file included from arch/mips/include/asm/mach-ip27/spaces.h:29:0,
                 from arch/mips/include/asm/page.h:12,
                 from arch/mips/vdso/vdso.h:26,
                 from arch/mips/vdso/gettimeofday.c:11:
arch/mips/include/asm/mach-generic/spaces.h:28:0: error: "CAC_BASE" redefined [-Werror]
 #define CAC_BASE  _AC(0x80000000, UL)

An earlier patch tried to make the second definition conditional,
but that patch had the #ifdef in the wrong place, and would lead
to another warning:

arch/mips/include/asm/io.h: In function 'phys_to_virt':
arch/mips/include/asm/io.h:138:9: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]

For all I can tell, there is no other reason than vdso32 to ever
include this file with CONFIG_32BITS set, and the vdso itself should
never refer to the base addresses as it is running in user space,
so adding an #ifdef here is safe.

Link: https://patchwork.kernel.org/patch/9418187/
Fixes: 3ffc17d8 ("MIPS: Adjust MIPS64 CAC_BASE to reflect Config.K0")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15039/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/mach-ip27/spaces.h

@@ -12,14 +12,16 @@
 
 /*
  * IP27 uses the R10000's uncached attribute feature.  Attribute 3 selects
- * uncached memory addressing.
+ * uncached memory addressing. Hide the definitions on 32-bit compilation
+ * of the compat-vdso code.
  */
-
+#ifdef CONFIG_64BIT
 #define HSPEC_BASE		0x9000000000000000
 #define IO_BASE			0x9200000000000000
 #define MSPEC_BASE		0x9400000000000000
 #define UNCAC_BASE		0x9600000000000000
 #define CAC_BASE		0xa800000000000000
+#endif
 
 #define TO_MSPEC(x)		(MSPEC_BASE | ((x) & TO_PHYS_MASK))
 #define TO_HSPEC(x)		(HSPEC_BASE | ((x) & TO_PHYS_MASK))