sh: remove -Werror from Makefiles

The sh build is full of warnings when building with gcc 9.2.1.  While
fixing those would be great, at least avoid failing the build.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Rich Felker <dalias@libc.org>

arch/sh/mm/Makefile

@@ -43,5 +43,3 @@ obj-$(CONFIG_UNCACHED_MAPPING)	+= uncached.o
 obj-$(CONFIG_HAVE_SRAM_POOL)	+= sram.o
 
 GCOV_PROFILE_pmb.o := n
-
-ccflags-y := -Werror