V4L/DVB (13969): frontends/si21xx.c: Remove #define TRUE/FALSE, use bool

And a little code refactoring/neatening around the removals

Reduces object size a little bit:

new:
$ size drivers/media/dvb/frontends/si21xx.o
   text	   data	    bss	    dec	    hex	filename
   8984	     56	   1816	  10856	   2a68	drivers/media/dvb/frontends/si21xx.o
old:
$ size drivers/media/dvb/frontends/si21xx.o
   text	   data	    bss	    dec	    hex	filename
   9084	     56	   1792	  10932	   2ab4	drivers/media/dvb/frontends/si21xx.o

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>