phase2: fix stray closing parenthesis

phase2: fix stray closing parenthesis

Due to the stray closing parenthesis introduced in commit f0faed2970dd
("phase2: compute checksums") we have currently we've failing checksum
step in phase2:

 argv: b'cd bin/packages/mipsel_24kc_24kf; find . -type f -not -name \'sha256sums\' -printf "%P\n" | sort | xargs -r ../../../staging_dir/host/bin/mkhash -n sha256 | sed -ne \'s!^\\(.*\\) \\(.*\\)$!\x01 *\x02!p\' > sha256sums)'
 environment:
  ...snip...
  using PTY: False
 /bin/sh: 2: Syntax error: ")" unexpected
 program finished with exit code 2

Fixes: f0faed2970dd ("phase2: compute checksums")
Reported-by: Hannu Nyman <hannu.nyman@iki.fi>
Signed-off-by: Petr Štetiar <ynezz@true.cz>