selftests/bpf: fix "valid read map access into a read-only array 1" on s390

This test looks up a 32-bit map element and then loads it using a 64-bit
load. This does not work on s390, which is a big-endian machine.

Since the point of this test doesn't seem to be loading a smaller value
using a larger load, simply use a 32-bit load.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -226,7 +226,7 @@
 	BPF_LD_MAP_FD(BPF_REG_1, 0),
 	BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
 	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1),
-	BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0),
+	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0),
 	BPF_EXIT_INSN(),
 	},
 	.fixup_map_array_ro = { 3 },