IB/ipath: Convert use of __constant_<foo> to <foo>

In little endian cases, the macros be16_to_cpu and cpu_to_be64
unfolds to __swab{16,64} which provides special case for constants.
In big endian cases, __constant_be16_to_cpu and be16_to_cpu
expand directly to the same expression. The same applies for
__constant_cpu_to_be64 and cpu_to_be64.

So, replace __constant_be16_to_cpu with be16_to_cpu and
__constant_cpu_to_be64 with cpu_to_be64, with the goal of getting
rid of the definition of __constant_be16_to_cpu and
__constant_cpu_to_be64 completely.

Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>