powerpc: Fix format string warning in arch/powerpc/boot/main.c

Fix format string warning in arch/powerpc/boot/main.c.  Also correct
a typo ("uncomressed") on the same line.

 BOOTCC  arch/powerpc/boot/main.o
arch/powerpc/boot/main.c: In function 'prep_kernel':
arch/powerpc/boot/main.c:65: warning: format '%08x' expects type
'unsigned int', but argument 3 has type 'long unsigned int'

Signed-off-by: Jon Smirl <jonsmirl@gmail.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>