lib/test_hmm.c: fix an error code in dmirror_allocate_chunk()

This is supposed to return false on failure, not a negative error code.

Fixes: 170e38548b81 ("mm/hmm/test: use after free in dmirror_allocate_chunk()")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dan Williams <dan.j.williams@intel.com>
Link: https://lkml.kernel.org/r/20201010200812.GA1886610@mwandaSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/test_hmm.c

@@ -461,7 +461,7 @@ static bool dmirror_allocate_chunk(struct dmirror_device *mdevice,
 
 	devmem = kzalloc(sizeof(*devmem), GFP_KERNEL);
 	if (!devmem)
-		return -ENOMEM;
+		return false;
 
 	res = request_free_mem_region(&iomem_resource, DEVMEM_CHUNK_SIZE,
 				      "hmm_dmirror");