misc: ibmasm: r_heartbeat: Demote function headers from kerneldoc

The correct format is not used and no attempt has been made
to document the function arguments.  Makes sense to just demote
the header back down to a simple comment.

Fixes the following W=1 warnings:

 drivers/misc/ibmasm/r_heartbeat.c:49: warning: Function parameter or member 'sp' not described in 'ibmasm_start_reverse_heartbeat'
 drivers/misc/ibmasm/r_heartbeat.c:49: warning: Function parameter or member 'rhb' not described in 'ibmasm_start_reverse_heartbeat'

Cc: "Max Asböck" <amax@us.ibm.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200701083118.45744-9-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/ibmasm/r_heartbeat.c

@@ -39,7 +39,7 @@ void ibmasm_init_reverse_heartbeat(struct service_processor *sp, struct reverse_
 	rhb->stopped = 0;
 }
 
-/**
+/*
  * start_reverse_heartbeat
  * Loop forever, sending a reverse heartbeat dot command to the service
  * processor, then sleeping. The loop comes to an end if the service