bcachefs: Better inlining for bch2_alloc_to_v4_mut

This separates out the slowpath into a separate function, and inlines
bch2_alloc_v4_mut into bch2_trans_start_alloc_update(), the main place
it's called.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
8 files changed