1. Use sbit UP = P^0; // it is more read able
2. there are no Port latch to read back from on 8052's
3. Why are you doing code in C you would not do in ASM?

in ASM
scan:JNB P0.7,scanup

JNB P0.6,scandown
...
SJMP scan


scanup:JNB P0.7,$
(...some codes...)

RET

scandown:JNB P0.6,$
(...some codes...)

RET

in C

void scan (void)
{
   if(P0^7)
   {
      (...some code...)
   }
   if(P0^6)
   {
      (...some code...)
   }
}

sbit is not the same a bit read the Manual.