xhci: Clean up ERST_PTR_MASK inversion

xhci: Clean up ERST_PTR_MASK inversion

Mathias notes that the ERST_PTR_MASK macro is named as if it's masking
the Event Ring Dequeue Pointer in the ERDP register, but in actuality
it's masking the inverse.

Invert the macro's value for clarity.

Migrate it to the modern GENMASK_ULL() syntax to avoid u64 casts.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20231019102924.2797346-10-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>