staging: sm750fb: avoid chained assignment in setcolreg()

Replace the chained assignment of red/green/blue with a temporary
variable and braces. This keeps behavior identical while improving
readability and satisfying checkpatch.

No functional change intended.

Signed-off-by: Cristian Del Gobbo <cristiandelgobbo87@gmail.com>
Link: https://patch.msgid.link/20251102230139.1720-2-cristiandelgobbo87@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: cris1618

drivers/staging/sm750fb/sm750.c

@@ -537,8 +537,13 @@ static int lynxfb_ops_setcolreg(unsigned int regno,
 		return -EINVAL;
 	}
 
-	if (info->var.grayscale)
-		red = green = blue = (red * 77 + green * 151 + blue * 28) >> 8;
+	if (info->var.grayscale) {
+		int lum = (red * 77 + green * 151 + blue * 28) >> 8;
+
+		red = lum;
+		green = lum;
+		blue = lum;
+	}
 
 	if (var->bits_per_pixel == 8 &&
 	    info->fix.visual == FB_VISUAL_PSEUDOCOLOR) {