ext4: remove duplicated #include of dax.h in inode.c

Fix following includecheck warning:
./fs/ext4/inode.c: linux/dax.h is included more than once.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220504225025.44753-1-yang.lee@linux.alibaba.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>