CHROMIUM: Input: cyapa - fix compile warning

CHROMIUM: Input: cyapa - fix compile warning

The string pointed to by fw_name is non-mutable, so make it const char *.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
BUG=chromium-os:36911
TEST=builds without following warning:
  drivers/input/mouse/cyapa.c: In function 'cyapa_update_fw_store':
  drivers/input/mouse/cyapa.c:1351:10: warning: assignment discards 'const' qualifier from pointer target type [enabled by default]

Change-Id: I43a3fc57a9462cece94d0c1db8011ae3084f8744
Reviewed-on: https://gerrit.chromium.org/gerrit/39934
Reviewed-by: Benson Leung <bleung@chromium.org>
Commit-Ready: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Tested-by: Daniel Kurtz <djkurtz@chromium.org>