powerpc/bpf ppc32: Fix JMP32_JSET_K

'andi' only takes an unsigned 16-bit value. Correct the imm range used
when emitting andi.

Fixes: 51c66ad8 ("powerpc/bpf: Implement extended BPF on PPC32")
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b94489f52831305ec15aca4dd04a3527236be7e8.1633464148.git.naveen.n.rao@linux.vnet.ibm.com

arch/powerpc/net/bpf_jit_comp32.c

@@ -1075,7 +1075,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 				break;
 			case BPF_JMP32 | BPF_JSET | BPF_K:
 				/* andi does not sign-extend the immediate */
-				if (imm >= -32768 && imm < 32768) {
+				if (imm >= 0 && imm < 32768) {
 					/* PPC_ANDI is _only/always_ dot-form */
 					EMIT(PPC_RAW_ANDI(_R0, dst_reg, imm));
 				} else {