include/kernel-defaults: set V='' if c is not set in OPENWRT_VERBOSE

include/kernel-defaults: set V='' if c is not set in OPENWRT_VERBOSE

This fixes the following errors:

  CALL    arch/powerpc/kernel/prom_init_check.sh
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer axpression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
arch/powerpc/kernel/prom_init_check.sh: line 39: [: ss: integer expression expected
  GEN     .version
  CHK     include/generated/compile.h
  UPD     include/generated/compile.h

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@31598 3c298f89-4303-0410-b956-a3cf2f4a3e73