cmd_mtdparts.c: fix compiler warning in debug code

Fix warning messages:
cmd_mtdparts.c:1429: warning: format '%08lx' expects type 'long
unsigned int', but argument 6 has type 'u32'
cmd_mtdparts.c:1429: warning: format '%08lx' expects type 'long
unsigned int', but argument 7 has type 'u32'

Signed-off-by: Wolfgang Denk <wd@denx.de>