fs/ntfs3: fix build without CONFIG_NTFS3_LZX_XPRESS

When CONFIG_NTFS3_LZX_XPRESS is not set then we get the following build
error:

  fs/ntfs3/frecord.c:2460:16: error: unused variable ‘i_size’

Signed-off-by: Mark O'Donovan <shiftee@posteo.net>
Fixes: 4fd6c08a

 ("fs/ntfs3: Use i_size_read and i_size_write")
Tested-by: Chris Clayton <chris2553@googlemail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>