net/mlx5: Refactor real time clock operation checks for PHC

net/mlx5: Refactor real time clock operation checks for PHC

Check if the MTUTC register of the NIC can be modified before attempting to
execute a real-time clock operation. Previous implementation aborted the
real-time clock operation pre-emptively when the MTUTC register used to
control the real-time clock was not modifiable, indicating real-time clock
mode was not enabled on the NIC. The original control flow was confusing
since the noop-if-RTC-disabled branch looked similar to an error handling
guard clause. The purpose of this patch is purely for improving readability
and should lead to no functional change.

Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>