[MIPS] Fix mprotect() syscall for MIPS32 w/36-bit physical address support

    
Fix mprotect() syscall for MIPS32 CPUs with 36-bit physical address
support: pte_modify() macro didn't clear the hardware page protection bits
before modifying...
Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

include/asm-mips/pgtable.h

@@ -354,6 +354,7 @@ static inline pgprot_t pgprot_noncached(pgprot_t _prot)
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
 	pte.pte_low  &= _PAGE_CHG_MASK;
+	pte.pte_high &= ~0x3f;
 	pte.pte_low  |= pgprot_val(newprot);
 	pte.pte_high |= pgprot_val(newprot) & 0x3f;
 	return pte;