OvmfPkg/IndustryStandard: make "Xen/grant_table.h" pure ASCII

OvmfPkg/IndustryStandard: make "Xen/grant_table.h" pure ASCII

The header file includes the UTF-8 encoding (0xE2 0x80 0x99) of the U+2019
(RIGHT SINGLE QUOTATION MARK) code point. Replace it with a simple
apostrophe (U+0027, ASCII 0x27).

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Thomas Huth <thuth@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>