ext4: Clean up calls to ext4_get_group_desc()

If the caller isn't planning on modifying the block group descriptors,
there's no need to pass in a pointer to a struct buffer_head.  Nuking
this saves a tiny amount of CPU time and stack space usage.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --cc fs/ext4/ialloc.c
Simple merge

diff --cc fs/ext4/super.c
Simple merge