vfs: only read fops once in fops_get/put

vfs: only read fops once in fops_get/put

In do_dentry_open() the usage is:
	f->f_op = fops_get(inode->i_fop);

In generated asm the compiler emits 2 reads from inode->i_fop instead of
just one.

This popped up due to false-sharing where loads from that offset end up
bouncing a cacheline during parallel open. While this is going to be fixed,
the spurious load does not need to be there.

This makes do_dentry_open() go down from 1177 to 1154 bytes.

fops_put() is patched to maintain some consistency.

No functional changes.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20240810064753.1211441-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>