lib/crc32.c: fix unused variables warnings

Variables t4, t5, t6 and t7 are only used when CRC_LE_BITS != 32.  Fix
the following compilation warnings:

  lib/crc32.c: In function 'crc32_body':
  lib/crc32.c:77:55: warning: unused variable 't7'
  lib/crc32.c:77:41: warning: unused variable 't6'
  lib/crc32.c:77:27: warning: unused variable 't5'
  lib/crc32.c:77:13: warning: unused variable 't4'

Signed-off-by: Thiago Rafael Becker <trbecker@trbecker.org>
Cc: "Darrick J. Wong" <djwong@us.ibm.com>
Cc: Bob Pearson <rpearson@systemfabricworks.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>