Replace val with __val in TUNABLE_SET_VAL_IF_VALID_RANGE

There are:

 #define TUNABLE_SET_VAL_IF_VALID_RANGE(__cur, __val, __type)                 \
({                                                                            \
  __type min = (__cur)->type.min;                                             \
  __type max = (__cur)->type.max;                                             \
                                                                              \
  if ((__type) (__val) >= min && (__type) (val) <= max)                       \
                                           ^^^ Should be __val
    {                                                                         \
      (__cur)->val.numval = val;                                              \
                            ^^^ Should be __val
      (__cur)->initialized = true;                                            \
    }                                                                         \
})

Luckily since all TUNABLE_SET_VAL_IF_VALID_RANGE usages are

TUNABLE_SET_VAL_IF_VALID_RANGE (cur, val, int64_t);

this didn't cause any issues.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>