MPC8xx: Fixup warning in arch/powerpc/cpu/mpc8xx/cpu.c

MPC8xx: Fixup warning in arch/powerpc/cpu/mpc8xx/cpu.c

cpu.c: In function ‘check_CPU’:
cpu.c:256:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Subject slightly changed.
Signed-off-by: Wolfgang Denk <wd@denx.de>
Tested on TQM855MDCBAB7-T66.102 (MPC855T at 66 MHz) and
TQM860LDB0A3-T50.202 (MPC860T at 50MHz).

Tested-by: Wolfgang Denk <wd@denx.de>
Acked-by: Wolfgang Denk <wd@denx.de>