anv: give more room to debug report

anv: give more room to debug report

The error buffer is limited to 256, but the report contains the
filename and possibly other data. So give it more space.

Avoids the warnings

../../src/intel/vulkan/anv_util.c: In function ‘__anv_perf_warn’:
../../src/intel/vulkan/anv_util.c:66:42: warning: ‘%s’ directive output may be truncated writing up to 255 bytes into a region of size 254 [-Wformat-truncation=]
    snprintf(report, sizeof(report), "%s: %s", file, buffer);
                                          ^~         ~~~~~~
../../src/intel/vulkan/anv_util.c:66:4: note: ‘snprintf’ output 3 or more bytes (assuming 258) into a destination of size 256
    snprintf(report, sizeof(report), "%s: %s", file, buffer);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

../../src/intel/vulkan/anv_util.c: In function ‘__vk_errorf’:
../../src/intel/vulkan/anv_util.c:96:48: warning: ‘%s’ directive output may be truncated writing up to 255 bytes into a region of size 252 [-Wformat-truncation=]
       snprintf(report, sizeof(report), "%s:%d: %s (%s)", file, line, buffer,
                                                ^~                    ~~~~~~
../../src/intel/vulkan/anv_util.c:96:7: note: ‘snprintf’ output 8 or more bytes (assuming 263) into a destination of size 256
       snprintf(report, sizeof(report), "%s:%d: %s (%s)", file, line, buffer,
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                error_str);
                ~~~~~~~~~~

Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>