video: fbdev: pvr2fb: initialize variables

clang static analysis reports this repesentative error

pvr2fb.c:1049:2: warning: 1st function call argument
  is an uninitialized value [core.CallAndMessage]
        if (*cable_arg)
        ^~~~~~~~~~~~~~~

Problem is that cable_arg depends on the input loop to
set the cable_arg[0].  If it does not, then some random
value from the stack is used.

A similar problem exists for output_arg.

So initialize cable_arg and output_arg.

Signed-off-by: Tom Rix <trix@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200720191845.20115-1-trix@redhat.com

drivers/video/fbdev/pvr2fb.c

@@ -1028,6 +1028,8 @@ static int __init pvr2fb_setup(char *options)
 	if (!options || !*options)
 		return 0;
 
+	cable_arg[0] = output_arg[0] = 0;
+
 	while ((this_opt = strsep(&options, ","))) {
 		if (!*this_opt)
 			continue;