[MIPS] Kexec: Fix several warnings.

arch/mips/kernel/machine_kexec.c: In function 'machine_kexec':
arch/mips/kernel/machine_kexec.c:54: warning: assignment makes integer from pointer without a cast
arch/mips/kernel/machine_kexec.c:70: warning: assignment makes integer from pointer without a cast
arch/mips/kernel/machine_kexec.c:81: warning: format '%08x' expects type 'unsigned int', but argument 2 has type 'long unsigned int'

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>