target/mips: avoid integer overflow in next_page PC check

If the PC is in the last page of the address space, next_page_start
overflows to 0. Fix it.
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Yongbok Kim <yongbok.kim@mips.com>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>

target/mips/translate.c

@@ -20202,14 +20202,14 @@ void gen_intermediate_code(CPUState *cs, struct TranslationBlock *tb)
     CPUMIPSState *env = cs->env_ptr;
     DisasContext ctx;
     target_ulong pc_start;
-    target_ulong next_page_start;
+    target_ulong page_start;
     int num_insns;
     int max_insns;
     int insn_bytes;
     int is_slot;
 
     pc_start = tb->pc;
-    next_page_start = (pc_start & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
+    page_start = pc_start & TARGET_PAGE_MASK;
     ctx.pc = pc_start;
     ctx.saved_pc = -1;
     ctx.singlestep_enabled = cs->singlestep_enabled;
@@ -20320,7 +20320,7 @@ void gen_intermediate_code(CPUState *cs, struct TranslationBlock *tb)
             break;
         }
 
-        if (ctx.pc >= next_page_start) {
+        if (ctx.pc - page_start >= TARGET_PAGE_SIZE) {
             break;
         }