udf: Fold udf_getblk() into udf_bread()

commit 32f123a3 upstream.

udf_getblk() has a single call site. Fold it there.

Signed-off-by: Jan Kara <jack@suse.cz>
[acsjakub: backport-adjusting changes
 udf_getblk() has changed between 6.1 and the backported commit, namely
 in commit 541e047b ("udf: Use udf_map_block() in udf_getblk()")
 Backport using the form of udf_getblk present in 6.1., that means use
 udf_get_block() instead of udf_map_block() and use dummy in buffer_new()
 and buffer_mapped(). ]
Closes: https://syzkaller.appspot.com/bug?extid=a38e34ca637c224f4a79


Signed-off-by: Jakub Acs <acsjakub@amazon.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>