kselftest: vDSO: Fix accumulation of uninitialized ret when CLOCK_REALTIME is undefined

kselftest: vDSO: Fix accumulation of uninitialized ret when CLOCK_REALTIME is undefined

[ Upstream commit 375b9ff53cb6f9c042817b75f2be0a650626dc4f ]

In the unlikely case that CLOCK_REALTIME is not defined, variable ret is
not initialized and further accumulation of return values to ret can leave
ret in an undefined state. Fix this by initialized ret to zero and changing
the assignment of ret to an accumulation for the CLOCK_REALTIME case.

Fixes: 03f55c7952c9 ("kselftest: Extend vDSO selftest to clock_getres")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>