fixed typo in phony declaration

Makefile

diff --git a/Makefile b/Makefile
index 65e6915..1aa9d25 100644
--- a/Makefile
+++ b/Makefile
@@ -168,7 +168,7 @@
 msp432:
 	PLATFORM=msp432 cargo build $(release) --target=thumbv7em-none-eabi --examples $(features)
 
-.PHONY: msp432
+.PHONY: flash-msp432
 flash-msp432:
 	PLATFORM=msp432 cargo run $(release) --target=thumbv7em-none-eabi --example $(EXAMPLE) $(features)