misc: ibmasm: r_heartbeat: Demote function headers from kerneldoc

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.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>