scripts: gen_isr_tables: fix pylint issues

pylint reports the following issues on the
scripts/build/gen_isr_tables.py:

 C0325:Unnecessary parens after '=' keyword (superfluous-parens)
File:scripts/build/gen_isr_tables.py
Line:16
Column:0
 C0325:Unnecessary parens after '=' keyword (superfluous-parens)
File:scripts/build/gen_isr_tables.py
Line:316
Column:0

Fix that so that unrelated PR touching the same file have a chance to
pass the compliance checks.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>