gallium/aux/tgsi/tgsi_parse.c: Fix two warnings

gallium/aux/tgsi/tgsi_parse.c: Fix two warnings

tgsi_parse.c: In function 'tgsi_parse_free':
tgsi_parse.c:54:31: warning: unused parameter 'ctx' [-Wunused-parameter]
    struct tgsi_parse_context *ctx )
                               ^~~
tgsi_parse.c: In function 'tgsi_parse_end_of_tokens':
tgsi_parse.c:62:25: warning: comparison between signed and unsigned
integer expressions [-Wsign-compare]
    return ctx->Position >=

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