tweaks for Xiaomi Redmi Note 9 'merlin'

audiojack, brightness, fp touches
  (thanks Akitake for reports)

rw-system.sh

@@ -367,10 +367,15 @@ if getprop ro.vendor.build.fingerprint | grep -q -i \
     -e xiaomi/nitrogen -e xiaomi/whyred -e xiaomi/platina \
     -e xiaomi/ysl -e nubia/nx60 -e nubia/nx61 -e xiaomi/tulip \
     -e xiaomi/lavender -e xiaomi/olive -e xiaomi/olivelite -e xiaomi/pine \
-    -e Redmi/lancelot -e Redmi/galahad; then
+    -e Redmi/lancelot -e Redmi/galahad -e Redmi/merlin; then
     setprop persist.sys.qcom-brightness "$(cat /sys/class/leds/lcd-backlight/max_brightness)"
 fi
 
+#Xiaomi Redmi Note 9
+if getprop ro.vendor.build.fingerprint |grep -qi -e Redmi/merlin; then
+    setprop persist.sys.overlay.devinputjack true
+fi
+
 #Realme 6
 if getprop ro.vendor.product.device |grep -iq -e RMX2001 -e RMX2151 -e RMX2111 -e RMX2111L1;then
     setprop persist.sys.phh.fingerprint.nocleanup true