pie: remove always false condition

pie: remove always false condition

When built with GCC warnings enabled:
q_pie.c: In function ‘pie_parse_opt’:
q_pie.c:78:38: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
        (alpha > ALPHA_MAX) || (alpha < ALPHA_MIN)) {
                                      ^
q_pie.c:85:35: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
        (beta > BETA_MAX) || (beta < BETA_MIN)) {
                                   ^

This is because MIN is 0 and unsigned number can never be less than 0.
Therefore just remove the _MIN values.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>