drivers/perf: arm_pmu: Fix some coding style issues

Fix some coding style issues reported by checkpatch.pl, including
following types:

ERROR: spaces required around that '=' (ctx:VxW)
WARNING: Possible unnecessary 'out of memory' message

Signed-off-by: Junhao He <hejunhao2@hisilicon.com>
Signed-off-by: Jay Fang <f.fangjian@huawei.com>
Link: https://lore.kernel.org/r/1620736054-58412-3-git-send-email-f.fangjian@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>