bpf, selftests: Fix spelling mistake "tained" -> "tainted"

There appears to be a spelling mistake in a bpf test message. Fix it.
Signed-off-by: NColin Ian King <colin.i.king@gmail.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211217182400.39296-1-colin.i.king@gmail.com

tools/testing/selftests/bpf/verifier/value_ptr_arith.c

@@ -1078,7 +1078,7 @@
 	.errstr_unpriv = "R0 pointer -= pointer prohibited",
 },
 {
-	"map access: trying to leak tained dst reg",
+	"map access: trying to leak tainted dst reg",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
 	BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),