x86 mpx: Change return type of get_reg_offset()

get_reg_offset() used to return the register contents themselves
instead of the register offset.  When it did that, it was an
unsigned long.  I changed it to return an integer _offset_
instead of the register.  But, I neglected to change the return
type of the function or the variables in which we store the
result of the call.

This fixes up the code to clear up the warnings from the smatch
bot:

New smatch warnings:
arch/x86/mm/mpx.c:178 mpx_get_addr_ref() warn: unsigned 'addr_offset' is never less than zero.
arch/x86/mm/mpx.c:184 mpx_get_addr_ref() warn: unsigned 'base_offset' is never less than zero.
arch/x86/mm/mpx.c:188 mpx_get_addr_ref() warn: unsigned 'indx_offset' is never less than zero.
arch/x86/mm/mpx.c:196 mpx_get_addr_ref() warn: unsigned 'addr_offset' is never less than zero.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/20141118182343.C3E0C629@viggo.jf.intel.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>