[S390] correct vdso version string

The glibc vdso code for s390 uses the version string 2.6.29, the
kernel uses the version string 2.6.26. No wonder the vdso code
is never used. The first kernel version to contain the vdso code
is 2.6.29 which makes this the correct version.
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/vdso.h

@@ -7,7 +7,7 @@
 #define VDSO32_LBASE	0
 #define VDSO64_LBASE	0
 
-#define VDSO_VERSION_STRING	LINUX_2.6.26
+#define VDSO_VERSION_STRING	LINUX_2.6.29
 
 #ifndef __ASSEMBLY__