fs/direct-io: remove redundant assignment to variable retval

fs/direct-io: remove redundant assignment to variable retval

The variable retval is being assigned a value that is not being read,
it is being re-assigned later on in the function. The assignment
is redundant and can be removed.

Cleans up clang scan build warning:
fs/direct-io.c:1220:2: warning: Value stored to 'retval' is never
read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20240410162221.292485-1-colin.i.king@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>