xfs: split xfs_bmap_btalloc
xfs: split xfs_bmap_btalloc

Split out the nullfb case into a separate function to reduce the stack
footprint and make the code more readable.

Signed-off-by: Christoph Hellwig <923f7720577207a44b32e59bbfbea59d27f1ae8e@lst.de>
Reviewed-by: Dave Chinner <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@fromorbit.com>
Signed-off-by: Alex Elder <f556392d917047d964350b9c68912016c96d5e94@sgi.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs