Fixes luminosity checks

They should now be more in-line with how they worked under the old
lighting system.

code/modules/hydroponics/seed.dm

@@ -281,7 +281,7 @@
 	if(!light_supplied)
 		var/atom/movable/lighting_overlay/L = locate(/atom/movable/lighting_overlay) in current_turf
 		if(L)
-			light_supplied = max(0,min(10,L.lum_r + L.lum_g + L.lum_b)-5)
+			light_supplied = L.get_clamped_lum()*10
 		else
 			light_supplied =  5
 

code/modules/hydroponics/trays/tray.dm

@@ -810,7 +810,7 @@
 			var/atom/movable/lighting_overlay/L = locate(/atom/movable/lighting_overlay) in T
 			var/light_available
 			if(L)
-				light_available = max(0,min(10,L.lum_r + L.lum_g + L.lum_b))
+				light_available = L.get_clamped_lum()*10
 			else
 				light_available =  5
 			light_string = "a light level of [light_available] lumens"