add hints for mips registers that may need restore

Signed-off-by: Jeffrey Martin <Jeffrey_Martin@rapid7.com>

include/mbedtls/bn_mul.h

@@ -750,7 +750,7 @@
         "sw     $10, %2         \n\t"   \
         : "=m" (c), "=m" (d), "=m" (s)                      \
         : "m" (s), "m" (d), "m" (c), "m" (b)                \
-        : "$9", "$10", "$11", "$12", "$13", "$14", "$15"    \
+        : "$9", "$10", "$11", "$12", "$13", "$14", "$15", "$lo", "$hi" \
     );
 
 #endif /* MIPS */