drm/amd/display: fix potential integer overflow when shifting 32 bit variable bl_pwm

The 32 bit unsigned integer bl_pwm is being shifted using 32 bit arithmetic
and then being assigned to a 64 bit unsigned integer.  There is a potential
for a 32 bit overflow so cast bl_pwm to enforce a 64 bit shift operation
to avoid this.

Addresses-Coverity: ("unintentional integer overflow")
Fixes: 3ba01817 ("drm/amd/display: Move panel_cntl specific register from abm to panel_cntl.")
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_panel_cntl.c

@@ -76,7 +76,7 @@ static unsigned int dce_get_16_bit_backlight_from_pwm(struct panel_cntl *panel_c
 	else
 		bl_pwm &= 0xFFFF;
 
-	current_backlight = bl_pwm << (1 + bl_int_count);
+	current_backlight = (uint64_t)bl_pwm << (1 + bl_int_count);
 
 	if (bl_period == 0)
 		bl_period = 0xFFFF;