ptp: ptp_clockmatrix: Demote non-kernel-doc header to standard comment

Fixes the following W=1 kernel build warning(s):

drivers/ptp/ptp_clockmatrix.c:1408: warning: Cannot understand * @brief Maximum absolute value for write phase offset in picoseconds
drivers/ptp/ptp_clockmatrix.c:1408: warning: Cannot understand * @brief Maximum absolute value for write phase offset in picoseconds
drivers/ptp/ptp_clockmatrix.c:1408: warning: Cannot understand * @brief Maximum absolute value for write phase offset in picoseconds
drivers/ptp/ptp_clockmatrix.c:1408: warning: Cannot understand * @brief Maximum absolute value for write phase offset in picoseconds
drivers/ptp/ptp_clockmatrix.c:1408: warning: Cannot understand * @brief Maximum absolute value for write phase offset in picoseconds

Cc: Richard Cochran <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/ptp/ptp_clockmatrix.c

···
 
 /* PTP Hardware Clock interface */
 
-/**
- * @brief Maximum absolute value for write phase offset in picoseconds
+/*
+ * Maximum absolute value for write phase offset in picoseconds
  *
  * Destination signed register is 32-bit register in resolution of 50ps
  *