lttng-libust: comma separate licenses

[Thomas: put between parenthesis the description of what is covered by
each license.]

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/lttng-libust/lttng-libust.mk

@@ -7,7 +7,7 @@
 LTTNG_LIBUST_SITE = http://lttng.org/files/lttng-ust
 LTTNG_LIBUST_VERSION = 2.7.1
 LTTNG_LIBUST_SOURCE = lttng-ust-$(LTTNG_LIBUST_VERSION).tar.bz2
-LTTNG_LIBUST_LICENSE = LGPLv2.1; MIT for system headers; GPLv2 for liblttng-ust-ctl/ustctl.c (used by lttng-sessiond)
+LTTNG_LIBUST_LICENSE = LGPLv2.1, MIT (system headers), GPLv2 (liblttng-ust-ctl/ustctl.c used by lttng-sessiond)
 LTTNG_LIBUST_LICENSE_FILES = COPYING
 
 LTTNG_LIBUST_INSTALL_STAGING = YES