arm64: vdso: update wtm fields for CLOCK_MONOTONIC_COARSE

Update wall-to-monotonic fields in the VDSO data page
unconditionally.  These are used to service CLOCK_MONOTONIC_COARSE,
which is not guarded by use_syscall.

Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>