Input: mt6779-keypad - move iomem pointer to probe function

Input: mt6779-keypad - move iomem pointer to probe function

The mmio base address is used for the only purpose of initializing
regmap for this driver, hence it's not necessary to have it in the
main driver structure, as it is used only in the probe() callback.
Move it local to function mt6779_keypad_pdrv_probe().

This commit brings no functional changes.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20220406115654.115093-1-angelogioacchino.delregno@collabora.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>