lib: remove redundant checks in get_u64 and get_s64

lib: remove redundant checks in get_u64 and get_s64

Static analyzer reported:
1. if (res > 0xFFFFFFFFFFFFFFFFULL)
Expression 'res > 0xFFFFFFFFFFFFFFFFULL' is always false , which may be caused by a logical error:
'res' has a type 'unsigned long long' with minimum value '0' and a maximum value '18446744073709551615'

2. if (res > INT64_MAX || res < INT64_MIN)
Expression 'res > INT64_MAX' is always false , which may be caused by a logical error: 'res' has a type 'long long'
with minimum value '-9223372036854775808' and a maximum value '9223372036854775807'
Expression 'res < INT64_MIN' is always false , which may be caused by a logical error: 'res' has a type 'long long'
with minimum value '-9223372036854775808' and a maximum value '9223372036854775807'

Corrections explained:
- Removed redundant check `res > 0xFFFFFFFFFFFFFFFFULL` in `get_u64`,
  as `res` cannot exceed this value due to its type.
- Removed redundant checks `res > INT64_MAX` and `res < INT64_MIN` in `get_s64`,
  as `res` cannot exceed the range of `long long`.

Triggers found by static analyzer Svace.

Signed-off-by: Anton Moryakov <ant.v.moryakov@gmail.com>
Signed-off-by: David Ahern <dsahern@kernel.org>