[CIFS] Memory leak in ntlmv2 hash calculation

 in function calc_ntlmv2_hash memory is not released.
1. If in the line 333 we successfully allocate memory and assign it to
pctxt variable:
       pctxt = kmalloc(sizeof(struct HMACMD5Context), GFP_KERNEL);
then we go to line 376 and exit wihout releasing memory pointed to by pctxt
variable.

Add a memory  releasing for pctxt variable before exit from function
calc_ntlmv2_hash.

Signed-off-by: Alexander Strakh <strakh@ispras.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>