x86: Disable -Werror

This is annoying during development and serves no useful purpose since
warnings are clearly displayed now that we are using Kbuild. Remove this
option.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/config.mk

@@ -7,7 +7,7 @@
 
 CROSS_COMPILE ?= i386-linux-
 
-PLATFORM_CPPFLAGS += -D__I386__ -Werror
+PLATFORM_CPPFLAGS += -D__I386__
 
 # DO NOT MODIFY THE FOLLOWING UNLESS YOU REALLY KNOW WHAT YOU ARE DOING!
 LDPPFLAGS += -DRESET_SEG_START=0xffff0000