bcachefs: remove redundant initialization of pointer dst

bcachefs: remove redundant initialization of pointer dst

The pointer dst is being initialized with a value that is never read,
it is being re-assigned later on when it is used in a while-loop
The initialization is redundant and can be removed.

Cleans up clang-scan build warning:
fs/bcachefs/disk_groups.c:186:30: warning: Value stored to 'dst' during
its initialization is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>