bash: changes to SIGINT handler while waiting for a child

bash: changes to SIGINT handler while waiting for a child

It rarely observes the problem while running shell script aborting
test repeatedly, at the problem, the test shell script never returns
to shell

Steps to reproduce:
1. Run test script and ctrl-c repeatedly
2. Observe whether returns to shell after ctrl-c

Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>