mm/shm: Fix ARCH_SHM_VEND
The last address is base+size-1
# define ARCH_SHM_MAXPAGES (CONFIG_ARCH_SHM_NPAGES * CONFIG_ARCH_SHM_MAXREGIONS)
# define ARCH_SHM_REGIONSIZE (CONFIG_ARCH_SHM_NPAGES * CONFIG_MM_PGSIZE)
# define ARCH_SHM_SIZE (CONFIG_ARCH_SHM_MAXREGIONS * ARCH_SHM_REGIONSIZE)
-# define ARCH_SHM_VEND (CONFIG_ARCH_SHM_VBASE + ARCH_SHM_SIZE)
+# define ARCH_SHM_VEND (CONFIG_ARCH_SHM_VBASE + ARCH_SHM_SIZE - 1)
# define ARCH_SCRATCH_VBASE ARCH_SHM_VEND
#else
