ptp: ptp_clockmatrix: fix is_single_shot

is_single_shot should return false for the power_of_2 mask

Fixes: bec67592

 ("ptp: ptp_clockmatrix: Add PTP_CLK_REQ_EXTTS support")
Signed-off-by: Min Li <min.li.xe@renesas.com>
Link: https://lore.kernel.org/r/1653403501-12621-1-git-send-email-min.li.xe@renesas.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>