gallium/aux/tgsi_aa_point.c: Fix -Wsign-compare warnings

gallium/aux/tgsi_aa_point.c: Fix -Wsign-compare warnings

tgsi/tgsi_aa_point.c:32:0:
tgsi/tgsi_aa_point.c: In Funktion »aa_decl«:
./util/u_math.h:660:29: Comparison between signed and unsigned in
conditional expressions [-Wsign-compare]
 #define MAX2( A, B )   ( (A)>(B) ? (A) : (B) )
                             ^
tgsi/tgsi_aa_point.c:76:21: Remark: when substituting of the macro
»MAX2«
       ts->num_tmp = MAX2(ts->num_tmp, decl->Range.Last + 1);
                     ^~~~
./util/u_math.h:660:40: Warning: signed and unsigned type in conditional
expression [-Wsign-compare]
 #define MAX2( A, B )   ( (A)>(B) ? (A) : (B) )
                                        ^
tgsi/tgsi_aa_point.c:76:21: Remark: when substituting of the macro
»MAX2«
       ts->num_tmp = MAX2(ts->num_tmp, decl->Range.Last + 1);
                     ^~~~
tgsi/tgsi_aa_point.c: In Funktion »aa_inst«:
tgsi/tgsi_aa_point.c:220:31: Comparison between signed and unsigned in
conditional expressions [-Wsign-compare]
           dst->Register.Index == ts->color_out) {

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>