may fail leading to a panic in bread().
Replace bread() with getblk() / VOP_STRATEGY() and return
an error if getblk() fails.
Fixes PR#46282: 6.0_BETA crash: msdosfs_bmap -> pcbmap -> bread -> bio_doread
This is an interim solution for easy pullup. The final solution
is be to change bread() to not return a buffer on error. As
we have to change all callers of bread() this will not qualify
for a pullup.
4856f6556b