Staging: xgifb: Fixed almost all style warnings.

I've removed all the warnings except one that I believe is a false
positive. The original author has used a macro to #define EXTERN to be
'extern', so in this case 'extern' is not used to define the storage
class of anything, but just the value of the macro. We can safely ignore
this warning.
Signed-off-by: NDaniel Kenji Toyama <kenji.toyama@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>