UBIFS: fix warning: format '%lX' expects type 'long unsigned int'

Commit 46d7274c "UBIFS: Change ubifsload to set the filesize variable"
introduced the follwing compiler warning:

ubifs.c: In function 'ubifs_load':
ubifs.c:742: warning: format '%lX' expects type 'long unsigned int', but argument 3 has type 'u32'

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Bastian Ruppert <Bastian.Ruppert@Sewerin.de>