different fix for "there are no lines to go on trainer:slave_mode"

Perhaps not the best solution from nice code point of view, but
from three ways I tried, it adds the least amount of bytes :)

src/general_menus.cpp

@@ -493,7 +493,7 @@ void menuProcTrainer(uint8_t event)
   uint8_t y;
   bool slave = SLAVE_MODE;
 
-  MENU(STR_MENUTRAINER, menuTabDiag, e_Trainer, slave ? 1 : 7, {0, 2, 2, 2, 2, 0/*, 0*/});
+  MENU(STR_MENUTRAINER, menuTabDiag, e_Trainer, slave ? 0 : 7, {0, 2, 2, 2, 2, 0/*, 0*/});
 
   if (slave) { // i am the slave
     lcd_puts(7*FW, 3*FH, STR_SLAVE);