multimedia/pwcbsd: Fix build under 14-CURRENT poudriere

Fix the following:

pwc-dec23.c:350:6: error: variable 'line_size' set but not used
[-Werror,-Wunused-but-set-variable]
        int line_size;          /* size of the line (4Y+U+V) */
            ^
pwc-dec23.c:608:17: error: variable 'pout' set but not used
[-Werror,-Wunused-but-set-variable]
        unsigned char *pout, *pout_planar_y = NULL, *pout_planar_u =
                       ^