misc: fix icc/clang compiler warnings

misc: fix icc/clang compiler warnings

clang warning:
libmount/src/tab.c:1833:6: warning: variable 'rc' is used uninitialized whenever
      'if' condition is true [-Wsometimes-uninitialized]
        if (!mpc)
            ^~~~

icc printf warnings:
    libmount/src/monitor.c(348): warning #2279: printf/scanf format not a string literal and no format arguments
            DBG(MONITOR, ul_debugobj(mn, status == 1 ? " success" : " nothing"));
            ^
    login-utils/vipw.c(348): warning #2279: printf/scanf format not a string literal and no format arguments
                           : _("You are using shadow passwords on this system.\n"));
                                                                                  ^

icc enum warnings:
    disk-utils/fdisk-menu.c(150): warning #188: enumerated type mixed with another type
            .exclude = FDISK_DISKLABEL_GPT | FDISK_DISKLABEL_BSD,
                       ^
    libsmartcols/src/table_print.c(750): warning #188: enumerated type mixed with another type
                            &width, align,
                                    ^

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>