src/main: remove unnecessary trailing backslashes
src/main: remove unnecessary trailing backslashes

Standard C string concatenation works fine here without escaping newline

Signed-off-by: Enrico Jorns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

ejoerns/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,jluebbe/rauc,rauc/rauc