gallium/aux/tgsi/tgsi_sanity.c: Fix warnings

tgsi_sanity.c: In function 'iter_instruction':
tgsi_sanity.c:316:29: warning: comparison between signed and unsigned
integer expressions [-Wsign-compare]
       if (ctx->index_of_END != ~0) {
                             ^~
tgsi_sanity.c: In function 'epilog':
tgsi_sanity.c:488:26: warning: comparison between signed and unsigned
integer expressions [-Wsign-compare]
    if (ctx->index_of_END == ~0) {

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Signed-off-by: Jakob Bornecrantz <jakob@collabora.com>

src/gallium/auxiliary/tgsi/tgsi_sanity.c

@@ -313,7 +313,7 @@ iter_instruction(
    uint i;
 
    if (inst->Instruction.Opcode == TGSI_OPCODE_END) {
-      if (ctx->index_of_END != ~0) {
+      if (ctx->index_of_END != ~0u) {
          report_error( ctx, "Too many END instructions" );
       }
       ctx->index_of_END = ctx->num_instructions;
@@ -486,7 +486,7 @@ epilog(
 
    /* There must be an END instruction somewhere.
     */
-   if (ctx->index_of_END == ~0) {
+   if (ctx->index_of_END == ~0u) {
       report_error( ctx, "Missing END instruction" );
    }