clk: gpio-gate: Include export.h instead of module.h

Include export.h for EXPORT_SYMBOL_GPL, no need to include module.h.

Cc: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Sergej Sawazki <ce3a@gmx.de>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>