serial: pch_uart: Remove unneeded NULL check

There is no need to do a NULL check for debugfs_remove().

Quoting Documentation/filesystems/debugfs.txt:

"The dentry value can be NULL, in which case nothing will be removed."

, so remove the unneeded NULL check.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>