staging/easycap: easycap_settings.c don't copy constant strings twice

eliminate copying twice a constant string just capture it using
const char * pointer

piggyback some other style fixes

Cc: Mike Thomas <rmthomas@sciolus.org>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>