drm/amd/display: fix a potential null pointer dereference

Currently the pointer init_data is dereferenced on the assignment
of fw_info before init_data is sanity checked to see if it is null.
Fix te potential null pointer dereference on init_data by only
performing dereference after it is null checked.

Addresses-Coverity: ("Dereference before null check")
Fixes: 9adc8050 ("drm/amd/display: make firmware info only load once during dc_bios create")
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c

@@ -1235,7 +1235,7 @@ static bool calc_pll_max_vco_construct(
 			struct calc_pll_clock_source_init_data *init_data)
 {
 	uint32_t i;
-	struct dc_firmware_info *fw_info = &init_data->bp->fw_info;
+	struct dc_firmware_info *fw_info;
 	if (calc_pll_cs == NULL ||
 			init_data == NULL ||
 			init_data->bp == NULL)
@@ -1244,6 +1244,7 @@ static bool calc_pll_max_vco_construct(
 	if (init_data->bp->fw_info_valid)
 		return false;
 
+	fw_info = &init_data->bp->fw_info;
 	calc_pll_cs->ctx = init_data->ctx;
 	calc_pll_cs->ref_freq_khz = fw_info->pll_info.crystal_frequency;
 	calc_pll_cs->min_vco_khz =