test: pr_cont_test.o depends on CONFIG_LOG=y

Compiling wandboard_defconfig with CONFIG_UT_LOG=y leads to a build error:

test/log/pr_cont_test.c: In function ‘log_test_pr_cont’:
test/log/pr_cont_test.c:28:14: error:
‘gd_t’ {aka ‘volatile struct global_data’} has no member named ‘log_fmt’
  log_fmt = gd->log_fmt;

We do not want to let CONFIG_UT_LOG depend on CONFIG_LOG=y because we have
tests for logging functions called with CONFIG_LOG=n.

Fix the build dependency.

Reported-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/test/log/Makefile b/test/log/Makefile
index afdafa5..3f09deb 100644
--- a/test/log/Makefile
+++ b/test/log/Makefile
@@ -8,7 +8,6 @@
 ifdef CONFIG_UT_LOG
 
 obj-y += test-main.o
-obj-y += pr_cont_test.o
 
 ifdef CONFIG_SANDBOX
 obj-$(CONFIG_LOG_SYSLOG) += syslog_test.o
@@ -16,6 +15,7 @@
 endif
 
 ifdef CONFIG_LOG
+obj-y += pr_cont_test.o
 obj-$(CONFIG_CONSOLE_RECORD) += cont_test.o
 else
 obj-$(CONFIG_CONSOLE_RECORD) += nolog_test.o