The pointer q is being assigned a value but it is never read. The
assignment and pointer are redundant and can be removed.
Cleans up clang scan build warning:

fs/bcachefs/quota.c:813:2: warning: Value stored to 'q' 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>