powerpc/xmon: Drop the valid variable completely in dump_segments()

The value of 'valid' is always zero when 'esid' is zero, and if 'esid'
is non-zero then the value of 'valid' is irrelevant because we are using
logical or in the if expression.

In fact 'valid' can be dropped completely from dump_segments() by
simply doing the check with SLB_ESID_V directly in the if.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
[mpe: Rewrite change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>