x86: Drop 4 unnecessary calls to __pa_symbol

x86: Drop 4 unnecessary calls to __pa_symbol

While debugging the __pa_symbol inline patch I found that there were a couple
spots where __pa_symbol was used as follows:
__pa_symbol(x) - __pa_symbol(y)

The compiler had reduced them to:
x - y

Since we also support a debug case where __pa_symbol is a function call it
would probably be useful to just change the two cases I found so that they are
always just treated as "x - y".  As such I am casting the values to
phys_addr_t and then doing simple subtraction so that the correct type and
value is returned.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Link: http://lkml.kernel.org/r/20121116215552.8521.68085.stgit@ahduyck-cp1.jf.intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>