arm64: stacktrace: Check kretprobe_find_ret_addr() return value

If kretprobe_find_ret_addr() fails to find the original return address,
it returns 0. Check for this case so that a reliable stacktrace won't
silently ignore it.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Andrea della Porta <andrea.porta@suse.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Song Liu <song@kernel.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-and-tested-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20250521111000.2237470-2-mark.rutland@arm.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>