display: set compiler option to print all warning messages

- Remove -Werror which would stop compilation, instead add -Wall
and -Wconversion, which would still print out the warning messages.
- Helps in fixing the warnings without breaking the compilation

Change-Id: Iffa4687a267d405a3011521f0882a9aefd88b5ce
diff --git a/common.mk b/common.mk
index ae4ea61..da38ded 100644
--- a/common.mk
+++ b/common.mk
@@ -24,7 +24,8 @@
 
 #Common C flags
 common_flags := -DDEBUG_CALC_FPS -Wno-missing-field-initializers
-common_flags += -Werror
+#TODO: Add -Werror back once all the current warnings are fixed
+common_flags += -Wconversion -Wall
 
 ifeq ($(ARCH_ARM_HAVE_NEON),true)
     common_flags += -D__ARM_HAVE_NEON