kernel/bpf/: Fix misspellings using codespell tool

A typo is found out by codespell tool in 34th lines of hashtab.c:

$ codespell ./kernel/bpf/
./hashtab.c:34 : differrent ==> different

Fix a typo found by codespell.
Signed-off-by: Liu xuzhi <liu.xuzhi@zte.com.cn>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210311123103.323589-1-liu.xuzhi@zte.com.cn

kernel/bpf/hashtab.c

@@ -31,7 +31,7 @@
 /*
  * The bucket lock has two protection scopes:
  *
- * 1) Serializing concurrent operations from BPF programs on differrent
+ * 1) Serializing concurrent operations from BPF programs on different
  *    CPUs
  *
  * 2) Serializing concurrent operations from BPF programs and sys_bpf()