dt-bindings: Fix typo on the DesignWare IP reset bindings documentation

This patch removes a loose "i" character is present on the current
documentation.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Link: https://lore.kernel.org/r/89719d8d40048e9b7baa0cd984b5bb108d056de4.1605741519.git.gustavo.pimentel@synopsys.com


Signed-off-by: Rob Herring <robh@kernel.org>