Add MobileError-related labels

This function is called from a few different places in the mobile code,
including from one special that is only executed when the
BattleTowerRoomMenu special returns with a non-zero code.

Since that special causes a blue "error" screen to appear, that looks
the exact same as the one you'd get when trying to connect from the
mobile trade corner/battle colosseum in a Pokémon Center's top floor,
and this function contains a bunch of japanese strings in a jumptable, I
think it's reasonable to assume it should be called
"DisplayMobileError".

misc/mobile_5f.asm

@@ -3003,7 +3003,7 @@ Function17e309: ; 17e309
 	call ClearScreen
 	call Function17e349
 	call Function17d5f6
-	callba Function17f555
+	callba DisplayMobileError
 	call Function17e349
 	call Function17dcaf
 	xor a
@@ -4623,7 +4623,7 @@ Function17f524: ; 17f524
 	jr .asm_17f536
 ; 17f53d
 
-Function17f53d: ; 17f53d
+BattleTowerMobileError: ; 17f53d
 	call FadeToMenu
 	xor a
 	ld [wc303], a
@@ -4632,7 +4632,7 @@ Function17f53d: ; 17f53d
 	ld a, $1
 	ld [rSVBK], a
 
-	call Function17f555
+	call DisplayMobileError
 
 	pop af
 	ld [rSVBK], a
@@ -4640,7 +4640,7 @@ Function17f53d: ; 17f53d
 	ret
 ; 17f555
 
-Function17f555: ; 17f555
+DisplayMobileError: ; 17f555
 .loop
 	call JoyTextDelay
 	call .RunJumptable