fat: cleanup fat_parse_long() error handling

Coverity CID 2332 & 2333 RESOURCE_LEAK

In fat_search_long() if fat_parse_long() returns a -ve value we return
without first freeing unicode.  This patch free's them on this error path.

The above was false positive on current tree, but this change is more
clean, so apply as cleanup.

[hirofumi@mail.parknet.co.jp: fix coding style]
Signed-off-by: Darren Jenkins <darrenrjenkins@gmail.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>