unitialized return value in mm/mlock.c: __mlock_vma_pages_range()

Fix an unitialized return value when compiling on parisc (with CONFIG_UNEVICTABLE_LRU=y):
	mm/mlock.c: In function `__mlock_vma_pages_range':
	mm/mlock.c:165: warning: `ret' might be used uninitialized in this function

Signed-off-by: Helge Deller <deller@gmx.de>
[ It isn't ever really used uninitialized, since no caller should ever
  call this function with an empty range.  But the compiler is correct
  that from a local analysis standpoint that is impossible to see, and
  fixing the warning is appropriate.  ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>