trigger/hrt: fix sysfs value propagation

The HRT trigger has a bug. If you program the fire in the past, the
trigger fires immediately, so ZIO has not the time to propagate the sysfs
value to the current_control. The result is that the acquired block has
the wrong value for attribute exp_{sec|scalar_h}.

The patch introduces a fire delay of 100ms when you program the trigger in the
past. This allows ZIO to propagate the sysfs values.

I am aware that 100ms can be a long time, but it does not matter because
the expected fire should be in the past and it is not possible. Moreover,
the cosistency of the control information will provide information about
the expected fire which is more important than rapidity of a wrong the fire.

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echo 3 > /sys/bus/zio/devices/zzero-0000/zero-input-32/trigger/exp-scalar-h
echo 4 > /sys/bus/zio/devices/zzero-0000/zero-input-32/trigger/exp-scalar-h

[ 1432.799476] zattr_store
[ 1432.799762]  trigger: writing value 3 to sysfs attribute exp-scalar-h
[ 1432.800183] ztt_conf_set:81
[ 1432.800466] ztt_conf_set:146
[ 1432.800846] ztt_fn:167
[ 1432.801162] zio_arm_trigger:131
[ 1432.801162] __zio_arm_input_trigger:82
[ 1432.801162] zbk_alloc_block:94
[ 1432.801162] zio_generic_data_done:135
[ 1432.801162] zbk_store_block:172 (ffff88000d4ebc00, ffff88000d40dd80)
[ 1432.803739] __zattr_propagate_value
[ 1435.736568] zattr_store
[ 1435.737977]  trigger: writing value 4 to sysfs attribute exp-scalar-h
[ 1435.739315] ztt_conf_set:81
[ 1435.740881] ztt_conf_set:146
[ 1435.742389] ztt_fn:167
[ 1435.743381] zio_arm_trigger:131
[ 1435.743381] __zio_arm_input_trigger:82
[ 1435.743381] zbk_alloc_block:94
[ 1435.743381] zio_generic_data_done:135
[ 1435.743381] zbk_store_block:172 (ffff88000d4ebc00, ffff88000d40df40)
[ 1435.747783] __zattr_propagate_value

From zio-dump

block 1 - "Ctrl: trigger-ext-5   0x00000002         2"
block 2 - "Ctrl: trigger-ext-5   0x00000003         3"
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Signed-off-by: Federico Vaga <federico.vaga@gmail.com>