perf script: Fix typo in branch event mask

BRACH -> BRANCH

Fixes: 88b14731 ("perf script: Separate events from branch types")
Signed-off-by: Yujie Liu <yujie.liu@intel.com>
Reviewed-by: Leo Yan <leo.yan@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Link: https://lore.kernel.org/r/20250312075636.429127-1-yujie.liu@intel.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>