switchtec: Fix SWITCHTEC_IOCTL_EVENT_IDX_ALL flags overwrite

In the ioctl_event_ctl() SWITCHTEC_IOCTL_EVENT_IDX_ALL case, we call
event_ctl() several times with the same "ctl" struct.  Each call clobbers
ctl.flags, which leads to the problem that we may not actually enable or
disable all events as the user requested.

Preserve the event flag value with a temporary variable.

Fixes: 52eabba5 ("switchtec: Add IOCTLs to the Switchtec driver")
Signed-off-by: Joey Zhang <joey.zhang@microchip.com>
Signed-off-by: Wesley Sheng <wesley.sheng@microchip.com>
[bhelgaas: changelog]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>