fs/hfsplus/extents.c: remove unused variable in hfsplus_get_block

The variable is defined but not used.  Generally it compiles away with
-O2 optimization hence it does not show a warning.

Signed-off-by: Sougata Santra <sougata@tuxera.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>