Don't leak fd when manipulating the device via _getdev()

Close the file descriptor when done calling ioctl with a try-finally block so
it doesn't get leaked.

MFC after:	2 months

tests/sys/opencrypto/cryptodev.py

@@ -122,10 +122,12 @@ class CryptAEAD(dpkt.Packet):
 CIOCCRYPTAEAD = 3225445229
 
 def _getdev():
-    fd = os.open('/dev/crypto', os.O_RDWR)
     buf = array.array('I', [0])
-    ioctl(fd, CRIOGET, buf, 1)
-    os.close(fd)
+    fd = os.open('/dev/crypto', os.O_RDWR)
+    try:
+        ioctl(fd, CRIOGET, buf, 1)
+    finally:
+        os.close(fd)
 
     return buf[0]