xhci: Preserve RsvdP bits in ERSTBA register correctly

xhci_add_interrupter() erroneously preserves only the lowest 4 bits when
writing the ERSTBA register, not the lowest 6 bits.  Fix it.

Migrate the ERST_BASE_RSVDP macro to the modern GENMASK_ULL() syntax to
avoid a u64 cast.

This was previously fixed by commit 8c1cbec9 ("xhci: fix event ring
segment table related masks and variables in header"), but immediately
undone by commit b17a57f8 ("xhci: Refactor interrupter code for
initial multi interrupter support.").

Fixes: b17a57f8

 ("xhci: Refactor interrupter code for initial multi interrupter support.")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org # v6.3+
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20230915143108.1532163-5-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>