befs: don't pass huge structs by value

'struct befs_disk_data_stream' is huge (~144 bytes) and it's being passed
by value in fs/befs/endian.h::cpu_to_fsrun().

It would be better to pass a pointer.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Cc: Will Dyson <will_dyson@pobox.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>