mesa: fix TexParameter functions

mesa: fix TexParameter functions

premature return in TexParameterf caused mesa to never call Driver.TexParameter
breaking drivers relying on this (fix bug #20966).
While here, also fix using ctx->ErrorValue when deciding to call
Driver.TexParameter. Errors are sticky and uncleared errors thus would cause
this to no longer get called. Since we thus need return value of
set_tex_parameter[if] can also optimize this to only call when value changed.