blobmsg/ulog: fix format string compiler warnings
Fixes following compiler warnings:
blobmsg.c:242:39: error: format string is not a string literal [-Werror,-Wformat-nonliteral]
blobmsg.c:248:23: error: format string is not a string literal [-Werror,-Wformat-nonliteral]
ulog.c:100:18: error: format string is not a string literal [-Werror,-Wformat-nonliteral]
ulog.c:112:16: error: format string is not a string literal [-Werror,-Wformat-nonliteral]
ulog.c:117:20: error: format string is not a string literal [-Werror,-Wformat-nonliteral]
Signed-off-by: Petr Štetiar <ynezz@true.cz>