loader/i386/bsd: Fix uninitialized scalar variable

loader/i386/bsd: Fix uninitialized scalar variable

In the function grub_netbsd_setup_video(), struct grub_netbsd_btinfo_framebuf
params is called but isn't being initialized. The member grub_uint8_t
reserved[16] isn't set to any values and is instead filled with junk data from
the stack. We can prevent this by setting params to {0}.

Fixes: CID 375026
Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>