firmware: fix google/gsmi duplicate efivars_sysfs_init()

Starting in commit e14ab23d,
efivars_sysfs_init() is called both by itself as an init function,
and by drivers/firmware/google/gsmi.c gsmi_init().

This results in runtime warnings such as the following:
[    5.651330] WARNING: at fs/sysfs/dir.c:530 sysfs_add_one+0xbd/0xe0()
[    5.657699] sysfs: cannot create duplicate filename '/firmware/gsmi/vars'

Fixing this by removing the redundant efivars_sysfs_init() call in
gsmi_init().

Tested: booted, checked that /firmware/gsmi/vars was still present and
showed the expected contents.

Signed-off-by: Michel Lespinasse <walken@google.com>
Acked-by: Matt Fleming <matt.fleming@intel.com>
Acked-by: Mike Waychison <mikew@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>