libcrc32c: Fix "crc32c undefined" compilation error

The latest shash changes leave crc32c undefined:

[...]
Building modules, stage 2.
  MODPOST 1381 modules
  ERROR: "crc32c" [net/sctp/sctp.ko] undefined!
  ERROR: "crc32c" [net/ipv4/netfilter/nf_nat_proto_sctp.ko] undefined!

Adding EXPORT_SYMBOL(crc32c) to lib/libcrc32c.c fixes the compile error.
This patch has been compile-tested only.
Signed-off-by: NAdrian-Ken Rueegsegger <rueegsegger@swiss-it.ch>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

lib/libcrc32c.c

@@ -57,6 +57,8 @@ u32 crc32c(u32 crc, const void *address, unsigned int length)
 	return *(u32 *)desc.ctx;
 }
 
+EXPORT_SYMBOL(crc32c);
+
 static int __init libcrc32c_mod_init(void)
 {
 	tfm = crypto_alloc_shash("crc32c", 0, 0);