xmalloc: correct _xmalloc_array() indentation

xmalloc: correct _xmalloc_array() indentation

It's been wrongly indented using tabs till now, and the stray blank
ahead of the final return statement gets in the way of using .i files
for detailed analysis of other compiler issues
(-Wmisleading-indentation kicks in due to the tab->space
transformation done in the course of pre-processing).

Also add missing spaces inside the if() at once, including the similar
case in _xzalloc_array().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>