libcacard: fix missing symbol in libcacard.so

Before patch:
$ make libcacard.la
$ nm ./libcacard/.libs/libcacard.so.0.0.0 | grep " U " | \
    egrep -v "(g_)|(GLIBC)|(SECMOD)|(PK11)|(CERT)|(NSS)|(PORT)|(PR)"
                 U error_set
Signed-off-by: NAlon Levy <alevy@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

libcacard/Makefile

@@ -7,7 +7,7 @@ libcacard_includedir=$(includedir)/cacard
 $(call set-vpath, $(SRC_PATH))
 
 # objects linked into a shared library, built with libtool with -fPIC if required
-QEMU_OBJS=$(oslib-obj-y) qemu-timer-common.o $(trace-obj-y) $(stub-obj-y)
+QEMU_OBJS=$(oslib-obj-y) qemu-timer-common.o error.o $(trace-obj-y) $(stub-obj-y)
 QEMU_OBJS_LIB=$(patsubst %.o,%.lo,$(QEMU_OBJS))
 
 # libtool will build the .o files, too