drm/amd/display: Initialize mode_select to 0

[WHAT]
mode_select was supposed to be initialized in mpc_read_gamut_remap but
is not set in default case. This can cause indeterminate
behaviors.

This is reported as an UNINIT error by Coverity.

Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Alex Hung

drivers/gpu/drm/amd/display/dc/mpc/dcn401/dcn401_mpc.c

@@ -561,7 +561,7 @@ void mpc401_get_gamut_remap(struct mpc *mpc,
 	struct mpc_grph_gamut_adjustment *adjust)
 {
 	uint16_t arr_reg_val[12] = {0};
-	uint32_t mode_select;
+	uint32_t mode_select = MPCC_GAMUT_REMAP_MODE_SELECT_0;
 
 	mpc_read_gamut_remap(mpc, mpcc_id, arr_reg_val, adjust->mpcc_gamut_remap_block_id, &mode_select);