drm/amd/display: Eliminate warnings in amdgpu_dm_helpers.c

Fix the following warnings reported by checkpatch:

WARNING: Block comments use a trailing */ on a separate line
WARNING: Prefer using '"%s...", __func__' to using 'execute_synaptics_rc_command', this function's name, in a string
WARNING: Prefer using '"%s...", __func__' to using 'apply_synaptics_fifo_reset_wa', this function's name, in a string
WARNING: braces {} are not necessary for single statement blocks

Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>