radeonsi: fix possible truncation on renderer string

Fixes truncation warning in gcc 8.1

Fixes: 8539c9bf31 ("gallium/radeon: add the kernel version into the renderer string")
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>

src/gallium/drivers/radeonsi/si_pipe.h

@@ -409,7 +409,7 @@ struct si_screen {
 
 	struct radeon_info		info;
 	uint64_t			debug_flags;
-	char				renderer_string[100];
+	char				renderer_string[183];
 
 	unsigned			gs_table_depth;
 	unsigned			tess_offchip_block_dw_size;