powerpc/vdso32: fix CLOCK_MONOTONIC on PPC64

[ Upstream commit dd9a994fc68d196a052b73747e3366c57d14a09e ]

Commit b5b4453e7912 ("powerpc/vdso64: Fix CLOCK_MONOTONIC
inconsistencies across Y2038") changed the type of wtom_clock_sec
to s64 on PPC64. Therefore, VDSO32 needs to read it with a 4 bytes
shift in order to retrieve the lower part of it.

Fixes: b5b4453e7912 ("powerpc/vdso64: Fix CLOCK_MONOTONIC inconsistencies across Y2038")
Reported-by: NChristian Zigotzky <chzigotzky@xenosoft.de>
Signed-off-by: NChristophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

arch/powerpc/kernel/vdso32/gettimeofday.S

@@ -98,7 +98,7 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime)
 	 * can be used, r7 contains NSEC_PER_SEC.
 	 */
 
-	lwz	r5,WTOM_CLOCK_SEC(r9)
+	lwz	r5,(WTOM_CLOCK_SEC+LOPART)(r9)
 	lwz	r6,WTOM_CLOCK_NSEC(r9)
 
 	/* We now have our offset in r5,r6. We create a fake dependency