arm64: perf: Remove unnecessary printk

ARM64 pmu prints an error message in event_init() when
no hardware PMU is available. This is pretty annoying as
it keeps printing the message for every single trial, flooding
the kernel logs, unnecessarily. The return code is sufficient for
the user to figure out the reason.

Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>