UPSTREAM: proc: bootconfig: Add null pointer check

kzalloc is a memory allocation function which can return NULL when some
internal memory errors happen. It is safer to add null pointer check.

Link: https://lkml.kernel.org/r/20220329104004.2376879-1-lv.ruyi@zte.com.cn



Bug: 254441685
Cc: stable@vger.kernel.org
Fixes: c1a3c360 ("proc: bootconfig: Add /proc/bootconfig to show boot config list")
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Lv Ruyi <lv.ruyi@zte.com.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
(cherry picked from commit bed5b60b)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I9309587524365ded06b7161e11e7220b89953066