Remove superfluous @ after \ in Makefile (#618)

Remove superfluous `@` in Makefile recipe lines that are split into
multiple lines using `\`:  only the first line should start with `@`
and it will apply to all the lines in the multi-line "recipe line";
if any other line in the "recipe line" starts with `@` it will be
considered as part of the command, resulting in errors such as
`/bin/sh: 3: @echo: not found`.

Co-authored-by: Javier Mora <[email protected]>

Makefile

@@ -156,11 +156,11 @@ verible:
 app: clean-app
 	@$(MAKE) -C sw PROJECT=$(PROJECT) TARGET=$(TARGET) LINKER=$(LINKER) LINK_FOLDER=$(LINK_FOLDER) COMPILER=$(COMPILER) COMPILER_PREFIX=$(COMPILER_PREFIX) ARCH=$(ARCH) SOURCE=$(SOURCE) \
 	|| { \
-	@echo "\033[0;31mHmmm... seems like the compilation failed...\033[0m"; \
-	@echo "\033[0;31mIf you do not understand why, it is likely that you either:\033[0m"; \
-	@echo "\033[0;31m  a) offended the Leprechaun of Electronics\033[0m"; \
-	@echo "\033[0;31m  b) forgot to run make mcu-gen\033[0m"; \
-	@echo "\033[0;31mI would start by checking b) if I were you!\033[0m"; \
+	echo "\033[0;31mHmmm... seems like the compilation failed...\033[0m"; \
+	echo "\033[0;31mIf you do not understand why, it is likely that you either:\033[0m"; \
+	echo "\033[0;31m  a) offended the Leprechaun of Electronics\033[0m"; \
+	echo "\033[0;31m  b) forgot to run make mcu-gen\033[0m"; \
+	echo "\033[0;31mI would start by checking b) if I were you!\033[0m"; \
 	exit 1; \
 	}