perf header: Fix spelling mistake "could't" -> "couldn't"

perf header: Fix spelling mistake "could't" -> "couldn't"

There is a spelling mistake in a pr_debug2 message. Fix it.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: kernel-janitors@vger.kernel.org
Link: https://lore.kernel.org/r/20220316232212.52820-1-colin.i.king@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>