py/asm*.c: Remove unnecessary check for num_locals<0 in asm entry func.

All callers of the asm entry function guarantee that num_locals>=0, so no
need to add an explicit check for it.  Use an assertion instead.

Also, the signature of asm_x86_entry is changed to match the other asm
entry functions.

py/asmarm.c

@@ -150,10 +150,7 @@ void asm_arm_bkpt(asm_arm_t *as) {
 //  | low address    | high address in RAM
 
 void asm_arm_entry(asm_arm_t *as, int num_locals) {
-
-    if (num_locals < 0) {
-        num_locals = 0;
-    }
+    assert(num_locals >= 0);
 
     as->stack_adjust = 0;
     as->push_reglist = 1 << ASM_ARM_REG_R1