tools/testing: check correct variable in open_procmap()

Check if "procmap_out->fd" is negative instead of "procmap_out" (which is
a pointer).

Link: https://lkml.kernel.org/r/aDbFuUTlJTBqziVd@stanley.mountain


Fixes: bd23f293 ("tools/testing: add PROCMAP_QUERY helper functions in mm self tests")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: levi.yun <yeoreum.yun@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>