avr32: Use block_sigmask()

avr32: Use block_sigmask()

Use the new helper function block_sigmask() which centralises the code
for updating current->blocked after successfully delivering a signal
and reduces the amount of duplicate code across architectures.

In the past some architectures got this code wrong, so using this
helper function should stop that from happening again.

Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Havard Skinnemoen <hskinnemoen@gmail.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>