x86/hvm: prevent gcc uninitialised var warning

x86/hvm: prevent gcc uninitialised var warning

gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3 reports:
----------------------------------------------------------------------
hvm.c: In function `hvm_create_ioreq_server':
hvm.c:487:18: error: `bufioreq_pfn' may be used uninitialised in this function
[-Werror=uninitialized]
hvm.c:718:30: note: `bufioreq_pfn' was declared here
----------------------------------------------------------------------

My code analysis says that gcc is wrong, but initilize the variable
to prevent the gcc warning.

Reported-by: Ian Murray <murrayie@yahoo.co.uk>
Signed-off-by: Don Slutz <dslutz@verizon.com>