broadcom: fix supported flag check in periodic output function

In bcm_ptp_perout_locked, the driver rejects requests which have
PTP_PEROUT_PHASE set. This appears to be an attempt to reject any
unsupported flags. Unfortunately, this only checks one flag, but does not
protect against PTP_PEROUT_ONE_SHOT, or any future flags which may be
added.

Fix the check to ensure that no flag other than the supported
PTP_PEROUT_DUTY_CYCLE is set.

Fixes: 7bfe91ef ("net: phy: Add support for 1PPS out and external timestamps")
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250312-jk-net-fixes-supported-extts-flags-v2-4-ea930ba82459@intel.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>