mesa: fix _mesa_texstore_argb8888() for MESA_FORMAT_XRGB8888
mesa: fix _mesa_texstore_argb8888() for MESA_FORMAT_XRGB8888

If we hit the general path and call _mesa_make_temp_chan_image() we
always want to get a GL_RGBA texture.  We were getting a 3-channel
GL_RGB texture before and that messed up the memory layout.

jbarczak/glsl-optimizer,mapbox/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,metora/MesaGLSLCompiler,benaadams/glsl-optimizer,KTXSoftware/glsl2agal,metora/MesaGLSLCompiler,benaadams/glsl-optimizer,mcanthony/glsl-optimizer,dellis1972/glsl-optimizer,benaadams/glsl-optimizer,jbarczak/glsl-optimizer,djreep81/glsl-optimizer,wolf96/glsl-optimizer,mapbox/glsl-optimizer,zz85/glsl-optimizer,mcanthony/glsl-optimizer,adobe/glsl2agal,mapbox/glsl-optimizer,zz85/glsl-optimizer,adobe/glsl2agal,zeux/glsl-optimizer,bkaradzic/glsl-optimizer,metora/MesaGLSLCompiler,KTXSoftware/glsl2agal,wolf96/glsl-optimizer,djreep81/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,adobe/glsl2agal,djreep81/glsl-optimizer,benaadams/glsl-optimizer,wolf96/glsl-optimizer,benaadams/glsl-optimizer,zeux/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,dellis1972/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,zeux/glsl-optimizer,bkaradzic/glsl-optimizer,KTXSoftware/glsl2agal,KTXSoftware/glsl2agal,adobe/glsl2agal,jbarczak/glsl-optimizer,adobe/glsl2agal,zz85/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,bkaradzic/glsl-optimizer,tokyovigilante/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,KTXSoftware/glsl2agal,wolf96/glsl-optimizer,mapbox/glsl-optimizer,tokyovigilante/glsl-optimizer,mcanthony/glsl-optimizer,zz85/glsl-optimizer,bkaradzic/glsl-optimizer