target/s390x: fix adj_len_to_page

adj_len_to_page doesn't return the correct result when the address
is already page aligned and the length is bigger than a page. Fix that.
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Message-Id: <20170531220129.27724-20-aurelien@aurel32.net>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

target/s390x/mem_helper.c

@@ -61,7 +61,7 @@ static inline uint32_t adj_len_to_page(uint32_t len, uint64_t addr)
 {
 #ifndef CONFIG_USER_ONLY
     if ((addr & ~TARGET_PAGE_MASK) + len - 1 >= TARGET_PAGE_SIZE) {
-        return -addr & ~TARGET_PAGE_MASK;
+        return -(addr | TARGET_PAGE_MASK);
     }
 #endif
     return len;