cns3xxx: don't use invalid mask value for clock events

cns3xxx: don't use invalid mask value for clock events

According to a commit from kernel 4.18-rc3, it's not valid
to use "cpu_mask_all" for clock events and it should be
replaced in favor of "cpu_possible_mask" [1]

This warning was seen when booting kernel 4.19 on a cns3xxx board.
Let's fix it also here just to be safe.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v4.19.18&id=fbfa9260085b5b578a049a90135e5c51928c5f7f

Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>