powerpc/8xx: Fix warning in hw_breakpoint_handler()

powerpc/8xx: Fix warning in hw_breakpoint_handler()

In hw_breakpoint_handler(), ea is set by wp_get_instr_detail() except
for 8xx, leading the variable to be passed uninitialised to
wp_check_constraints().  This is safe as wp_check_constraints() returns
early without using ea, so just set it to make the compiler happy.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221024041346.103608-1-ruscur@russell.cc