Merge pull request #8274 from tcm0116/2.0.x-re_arm_D8

[2.0.x] Correct RAMPS_D8_PIN for Re-ARM

Marlin/src/pins/pins_RAMPS_RE_ARM.h

   #define MOSFET_D_PIN   -1
 #endif
 #ifndef RAMPS_D8_PIN
-  #define RAMPS_D8_PIN   P2_8
+  #define RAMPS_D8_PIN   P2_7
 #endif
 #ifndef RAMPS_D9_PIN
   #define RAMPS_D9_PIN   P2_4