gallium/radeon: handle failure when mapping staging buffer
gallium/radeon: handle failure when mapping staging buffer

Cc: "11.1 11.2" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>
Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler