drm/amd/display: drop redundant memset() in get_available_dsc_slices()

get_available_dsc_slices() returns the number of indices set, and all of
the users of get_available_dsc_slices() don't cross the returned bound
when iterating over available_slices[]. So, the memset() in
get_available_dsc_slices() is redundant and can be dropped.

Fixes: 97bda0322b8a ("drm/amd/display: Add DSC support for Navi (v2)")
Reported-by: Christophe JAILLET <[e-mail]>
Reviewed-by: Rodrigo Siqueira <[e-mail]>
Signed-off-by: Hamza Mahfooz <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c

···
 {
 	int idx = 0;
 
-	memset(available_slices, -1, MIN_AVAILABLE_SLICES_SIZE);
-
 	if (slice_caps.bits.NUM_SLICES_1)
 		available_slices[idx++] = 1;