[S390] Implement ext2_find_next_bit.

Fixes this compile error:

fs/ext4/mballoc.c:
	In function 'ext4_mb_generate_buddy':
fs/ext4/mballoc.c:954:
	error: implicit declaration of function 'generic_find_next_le_bit'

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>