drivers/perf: arm_dsu_pmu: Remove kerneldoc-style comment syntax

For some reason, the Arm DSU PMU driver uses kerneldoc-style comment
syntax (i.e. /** ) for non-kerneldoc comments. This makes the robots
very angry indeed, so just revert these to normal comments to stop
the noise.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202312092000.8ltwotjt-lkp@intel.com/


Signed-off-by: Will Deacon <will@kernel.org>