drm/i915: Fix format for perf_limit_reasons

Use hex format so that it is easier to decode.

Fixes: fe597966

 ("drm/i915/debugfs: Add perf_limit_reasons in debugfs")
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230315022906.2467408-1-vinay.belgaumkar@intel.com