staging: easycap: fix sparse warnings :conversion of int to enum

easycap_settings.c:587:58: warning: conversion of
easycap_settings.c:587:58:     unsigned int to
easycap_settings.c:587:58:     int enum v4l2_field
easycap_settings.c:593:63: warning: conversion of
easycap_settings.c:593:63:     unsigned int to
easycap_settings.c:593:63:     int enum v4l2_colorspace

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