fs/squashfs/file_direct.c: replace count*size kmalloc by kmalloc_array

kmalloc_array() manages count*sizeof overflow.

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Cc: Phillip Lougher <phillip@squashfs.org.uk>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>