gpio: pca953x: Fix warning when HW interrupts are rescheduled by the softirq tasklet

gpio: pca953x: Fix warning when HW interrupts are rescheduled by the softirq tasklet

When using the matrix_keymap driver with the gpio-pca953x driver, the
following warning may be issued when a keypress is detected:
WARNING: CPU: 0 PID: 3 at kernel/irq/manage.c:677 irq_nested_primary_handler+0x18/0x2c()
Primary handler called for nested irq 245
Modules linked in: evbug ci_hdrc_imx usbmisc_imx ci_hdrc udc_core ehci_hcd phy_mxs_usb
CPU: 0 PID: 3 Comm: ksoftirqd/0 Tainted: G        W     3.16.0-karo+ #118
[<c00142cc>] (unwind_backtrace) from [<c00118f8>] (show_stack+0x10/0x14)
[<c00118f8>] (show_stack) from [<c001bf10>] (warn_slowpath_common+0x64/0x84)
[<c001bf10>] (warn_slowpath_common) from [<c001bfc4>] (warn_slowpath_fmt+0x30/0x40)
[<c001bfc4>] (warn_slowpath_fmt) from [<c004ce08>] (irq_nested_primary_handler+0x18/0x2c)
[<c004ce08>] (irq_nested_primary_handler) from [<c004cb80>] (handle_irq_event_percpu+0x50/0x168)
[<c004cb80>] (handle_irq_event_percpu) from [<c004ccf8>] (handle_irq_event+0x60/0x7c)
[<c004ccf8>] (handle_irq_event) from [<c004f02c>] (handle_simple_irq+0x78/0xdc)
[<c004f02c>] (handle_simple_irq) from [<c004ed14>] (resend_irqs+0x4c/0x78)
[<c004ed14>] (resend_irqs) from [<c001f3ec>] (tasklet_action+0x74/0xd8)
[<c001f3ec>] (tasklet_action) from [<c001f760>] (__do_softirq+0xd0/0x1f4)
[<c001f760>] (__do_softirq) from [<c001f8c4>] (run_ksoftirqd+0x40/0x64)
[<c001f8c4>] (run_ksoftirqd) from [<c003d464>] (smpboot_thread_fn+0x174/0x234)
[<c003d464>] (smpboot_thread_fn) from [<c0036dd4>] (kthread+0xb4/0xd0)
[<c0036dd4>] (kthread) from [<c000f0f0>] (ret_from_fork+0x14/0x24)
---[ end trace a68cf7bc5348c4f7 ]---

This happens when an IRQ is detected by the GPIO driver while the GPIO
client driver (matrix_keypad in this case) has disabled the irq for
the GPIO it has acquired. When the HW IRQ is being rescheduled by the
softirq thread, the primary IRQ handler is called for the nested IRQ.

This patch makes sure, that the parent_irq (gpio-pca953x) is
rescheduled rather than the nested irq registered by the matrix_keypad
driver.
Similar patches are most probably required for a bunch of other
drivers too.